He's fast, yeah, but I'm not seeing great feet from what I've watched. I worry about his footwork and technique, along with his frame, the two of which together could give him a ton of trouble getting off the LOS against press. And if he can't get off press coverage, his speed is entirely moot.
The team has had issues with compressed fields for awhile, so the speed sounds nice, but more than that I'd like a WR who can consistently compete with tight man coverage and I'm not sure Thornton can do that at the moment. His feet look a little slow, a little heavy, not particularly light on his feet, doesn't have that effortless smoothness you hope to see, and doesn't seem efficient getting off the LOS and making cuts/breaks. His feet look choppy and not in a good way.
This feels similar to previous WR picks, like Jackson/Johnson/Harry -- a guy with some unique skill/talent, but not a well-rounded/polished WR to my eye. That's why if they went with a WR I wanted it to be Metchie; he is insanely polished, has phenomenal feet, knows the position well, can line up anywhere, and has the footwork/technique/savvy to destroy man coverage.
Maybe others see him as a more polished and developed WR. I'll watch more and hopefully come around on the guy.
Meh ...