The Shewee is not flexible, and as far as I can tell is hard polypropylene, not silicone.
I've used one a few times, including the extension tube. As Charlotte says, this is basically just a few inches of PVC pipe which can be fitted to the funnel. They're a bit 'meh,' but seem to work ok for me. Practice is required, but I have no idea why they recommend trying it in the shower - you don't even stand the same way in the shower. Practice should be done whilst wearing real clothes, and that way you get a sense of how to hold the damn thing without it leaking all down your leg and into your shoe. Do not ask me how I know this.
It's a one-size-fits-all unit, which doesn't fit anyone as far as I can see, but it does address the question of how/where to pee without hiding in the bushes for those of us that are largely flush decked and have hip/back flex issues.
You might also find a use for cleansing wipes and hand sanitiser if you're going to use one on a camping tour where you can't easily clean and dry it. Oh, and sand off the moulding flash before you use it. Trust me on this.