Looking at the receivers, Jordan Matthews and Sammy Watkins have 3 years of comparable production. This is mostly because of Sammy's durability concerns. I'm not telling you Matthews is a better player, but I will say that Matthews has consistently shown us 70-80 catches and 800 yards are so. Sammy has more upside than that, minus whatever justifiable durability concerns anybody has. I'd say a second round pick, especially from a team like the Rams, is absurdly good value and I would much rather gamble on the high pick than gamble on Watkins' health, especially at a position that has exactly zero impact on a team's win total. Buffalo probably wins seven to nine games with Watkins on the team, and probably wins seven to nine games without him on the team. From that standpoint, I think it's a good deal because the second round pick allows Buffalo to bring in another talent without much productivity cost.
The Darby one, I'm not really sure. Buffalo brings back a guy who can start and takes another early-ish pick from a team that isn't very good.
At the end, I think Buffalo is probably as good after the trade as they were before it. Now they have 6 picks in the first three rounds and can get another compensatory 3 if they move certain pieces around. This means they can get much younger in a hurry or move up to get a QB while taking a shot at the wild card this year. It's a sound philosophy IMO.