I have they Empire knee pads that are full length and cover your shins as well. They work well, but get a bit hot during the summer. I tried the Dye C8 knee pads. Those have the best padding of any pads I've tried, but after a few superman dives, they slip down to my ankles.
The PE knee pads do look a bit cheap in comparison to the Dye C8's. They seem almost like volleyball pads. But they also cost $15 less. And once I put them on, they stay put. They do not slip at all, no matter how much I dive.
They run a bit big. I ordered large, but they were too big. I ordered medium and they fit perfectly except for the top strap which was too tight. I don't even bother velcro'ing the top strap and they still don't slip.
Conclusion:
Despite looking cheap and not as high tech as some other pads out there, they stay put better than any pads I've tried. And isn't that the point of knee pads? To stay where you put them to help protect your knees? I would definitely say give them a try if you're tired of continuously having to pull your knee pads up throughout the day.
