Now I've used it in anger, I thought I'd write a proper review...
Sleeping bags are tricky. Due to the strong correlation between demand for good thermal properties and demand for light weight and small pack size, you're pretty much restricted to 'mummy' shaped bags if you want something with decent performance. Rectangular down-filled mats are expensive unobtanium, and only really come from the US in larger sizes.
This isn't a problem if you're lucky enough to be able to sleep in something that restrictive. I generally don't - not just because I have a dodgy knee that sometimes seizes up painfully and needs to be fully flexed/extended in the night, but also because I tend to suffer from lower back ache if I can't spread my hips far enough apart to distribute the load naturally.
Until now I've managed with one of two cheap synthetic bags - if it's just a night in warm conditions (so that unzipping the lower section and sticking a leg out is feasible) I've used a lightweight mummy-style bag and accepted poor sleep. Otherwise, I've used a decent thickness rectangular bag - often with a silk liner - and lived with it being heavy and filling a whole large pannier.
Enter the Dreamcatcher... Someone on here pointed me at them after a conversation at the Andover camping trip last year, and I've been wibbling about them on and off ever since. A couple of weeks ago I saw one at a decent price in a sale and decided to take the plunge. Being 167cm tall, I bought the women's 650 model:
The unique feature about this design is that while it's ostensibly mummy-shaped, the section between waist and ankles is in fact cut much wider, with elasticated baffles that gently compress it back to the default mummy shape. This means that your legs are free to move apart from each other inside the bag, and rest at whatever angle is most comfortable. When they're closer together the elastic gently brings the sides of the bag in to maximise the insulation properties.
This works astoundingly well - while it doesn't allow me to spread my knees as wide as they will go, it does allow for the maximum separation that I'd consider comfortable enough to sleep in. The foot section is still narrow, so you generally end up with either your feet together in the foot section, or one leg bent with the foot alongside the other (extended) leg - you can't sleep with your legs in a V-shape without opening the zip. In practice, I don't find this a problem - What I usually want to do is sleep on my back with my knees roughly shoulder-width apart, and the dodgy one optionally elevated by a stuff-sack of spare clothes under the sleeping bag, or on my side with both legs bent in a standard mummy-bag-compatible way.
As a result of the baffle design, the most restrictive part of the bag is around the elbows. I find there's enough room in the upper section for all the arm-movement I'm likely to need (jibbling liners, removing clothing, operating a mobile phone without getting cold hands and so on are perfectly achievable).
That cleverness aside, it's an extremely well thought-through piece of kit: The foot section is warm (apparently there's more foot insulation in the women's versions) and actually foot-shaped. The hood section Just Works in a way the ones on my cheaper bags never did - the opening closes down leaving your eyes, nose and mouth exposed, rather than your chin and a section of neck. There are down-filled flaps that overlap the zips and enclose your shoulders, preventing heat loss - these are extremely effective in use. The zips appear robust and are generally easy to use, though because of the thermal padding doing up the last 30cm or so from the inside of the bag can be a bit tricky - it's actually easier to keep one arm out and do it up from the outside. There are actually two seperate zips, which meet a little above ankle-height. This is apparently intended so that two bags may be joined together while preserving the shape of their respective foot areas - only having the one bag I can't test this. But what it does mean is that you can open the foot section for ventilation without the whole thing unzipping itself in the night, or you can unzip the leg section to stick a foot out of, and have an intact warm foot section to stick it back into when it gets a bit chilly. As someone who tends to use one foot as a heatsink in bed, I wholeheartedly approve. There's also what barakta deemed "a hearing aid pocket" - a wallet-sized pocket on the inside of the upper section at chest height, for items that are valuable or need to be easy to find in the dark. I haven't tested whether a vibrating gadget stowed in this pocket would wake you reliably, but if you're careful you can sleep on either side without being knobbled by its contents.
I've used it for a couple of nights on a recent camping trip where it got down to about 8-9C at night, in combination with the now legendary Exped Downmat. Wearing only a T-shirt, I found the temperature on the cool side of comfortable. On the second night I added a silk liner (mainly on the basis that my trousers were a bit muddy) and was Just Right until about 5am, at which point I woke up, swore at the local poultry, wriggled out of the liner and unzipped the foot section, and enjoyed another 3 hours of decent sleep.
I expect that with a liner and a more usual amount of clothing (especially tactical use of socks and buffs) it would be comfortable in much colder temperatures. As it warms up, it's easy to regulate temperature by opening the hood and zips, without finding yourself completely out of the bag. I've yet to try it indoors, I suspect it may be a bit too warm for summer room temperatures.
What else? It comes with a stuff-sack which seems to be generic across models; the women's 650 is a fairly easy fit (if you're used to synthetic bags, the sheer compressibility of down will come as a surprise), so I assume the larger models would require a bit more stuffing effort. The stuff-sack is sturdy and fleece-lined with a separate drawstring on the inside for use as a pillow when inverted. I found that with a bit of practice I could inflate my £2 decathlon inflatable pillow inside it, close the drawstring and have something as comfortable as an Ajungilak, albeit rectangular. This was an unexpected bonus.
It's also supplied with a large netting storage bag (down works best if uncompressed for long-term storage), and several sachets of silica gel. I mention these only because if you don't know to look for them, you'll probably find one nestling in your crevices on the first night.
The colour is (in my humble and somewhat colourblind opinion) significantly less bad (read: girly) than it appears in the picture. Your height-appropriate model and sense of aesthetics will vary. Speaking of height, the max height on the 650W is quoted as 175cm, and I find the fit pretty much perfect - so the quoted height figures seem realistic.
In summary then: if you want a performance sleeping bag that doesn't restrict your legs, it's hard to fault. At some 500g lighter, significantly warmer and massively smaller-packing than my rectangular synthetic bag it's subjectively lightweight, though rock'ard mummy-bag users will probably scoff at the weight. As with the Downmat and the thicker Alpkit Airics, I consider the weight/bulk to be a reasonable trade-off for a decent night's sleep on anything but a S24O. I know I'm not alone in this philosophy.
ETA:I've now had reason to use this - again in combination with a Downmat - indoors (in June, so at a comfortable room temperature). Wearing just a T-shirt, with the foot compartment zip open and without making use of the hood (other than as a convenient pillow-restraint) the temperature was just on the warm side of comfortable. Optimal comfort was achieved by unzipping the main compartment and sticking the right amount of limbs out to regulate temperature. I would have been better off with a thin synthetic bag, or maybe just a liner and a few more clothes. Which is about what I expected, really.
