FIT: No slippage. I have chicken legs and ordered the smalls. Had to take the adjustable strap all the way in but fit is perfect. Front of guard rides about 1/8 of an inch off the front of the shin when leg is straightened which allows for excellent venting.
Function: I've taken a number of light spills in them and had no issues whatsoever. VPD material they are working with is crazy! Works just like they claim, moldable when riding and solid on impact! Actually aim for my knees and elbows now.
Build: This is actually why I bought these and I've only been more impressed since I've put them to use. For how well they work, they are extremely simple in design and not overbuilt like many of the other pads on the market. I have quite a few friends that are very glad they got their current armor on sale because they are turning around and hunting down POC products.
As an ender I just have to commend Huck n Roll on their service. The first pair I got had 2 different sized legs in the box and I didn't notice until after I had used the things. Not only did they send me a new pair that arrived within 48 hours but they paid for return shipping of the 1st set without any questions asked. Thanks Huck n Roll!