I got these, along with the POC Bone Arm, and I'm very happy. The best part about them is the articulated joint that allows for great freedom of movement. I'm 6'1" and 180lbs, and I went with the large size. I found once I started riding, they would slide down a bit from my initial placement, but not much, and once they settled in there was no further movement. I've found that other pads fit fine when your leg is straight, then constrict when you bend your knee. That is not the case with these, as they are made of two segments with a stitched joint. It makes for a very nice feel when pedaling.
No crashes yet, so I can't comment on the impact protection.
They are hardshell pads, so there is some warmth and weight to deal with, but they aren't bad at all.
They are designed as step-in/slide-on pads, with a small segment at the top of the pad that wraps around your leg, just above the knee. These can be worn without stepping in or sliding on, by just using the velcro straps. There a thigh strap, an ankle strap, and a calf strap. The calf strap is a nice design with much adjustment that allows a very comfortable fit.
It has been mentioned by others, and I found this to be the case as well, when you bend your knee, the hardshell portion of the pad stays fixed over the patella, and only the "dough" portion of the pad moves to cover the top of the knee. It doesn't give me any concerns, as the "dough" portion of the pad seems like it will be enough to protect on an impact. It has also been noted that the inside/outside of knee coverage isn't as good as it could be. I will agree that it appears the pads could wrap around a bit more, but it isn't such that I'd call it a bad design.
Overall, the most comfortable pads I've worn, with the best range of motion and least slippage. Certainly not cheap, but worth it if they hold up and last.