So far they're great. These are a big step up, protection wise, from pads like the Fox Enduros (which don't have the gel pads), but they're just as comfy for pedaling. Less of a pain to get on and off than the G-Forms, and way sturdier (those tend to rip after snagging on stuff). The only gripe I have is that the silicon grippers are almost too effective for hairy legs.
I'm coming off a pair of POC VPD 2.0s, which protection wise are more along the lines of the slightly beefier Hellion (got a pair of those as well). I loved those pads, but they started stretching out and not staying in place. The Slayers are great for all around trail riding; I use the Hellions when I ride rowdier stuff (they're great as well - bit warmer, bit less unobtrusive, but pretty bombproof on the protection end of things).
Well made, comfy, doing their job. Only have about 30-ish hours riding in them yet, so too early to tell about durability.