Used them on a 200 at the weekend and I think I like them. The position is surprisingly different to tri-bars but I did feel the similar 1mph or so boost in speed that I would get on the tri-bars.
One nice thing about the position was that because it's not as tucked it was good for getting my shoulders on my back and giving them a nice stretch.
I found I could sustain relatively long periods (10 minutes or so) with the forearms resting on the top bars and didn't find it particularly uncomfortable at all really.
They're certainly great for give a variety of hand positions - holding the fronts, with forearms on the tops, holding the fronts arms outstretched, and holding onto the sides. I appreciated that variety particularly towards the end of the ride when the aches and pains were getting a bit more noticeable.
I'm going to keep them on the bike for now, first impressions definitely positive.