I have several different brands of folding rear sights on my ARs and here’s my opinions on them in no particular order…. Troy, YHM (old style and new style), ARMS, Wilson
I think everyone agrees that the Troy’s one of the best, both rugged and streamlined. They are hard to find and nobody seem to be able to keep them in stock here. Since they are over the $100 ITAR max they are hard to import.
The new style YHM are very similar to the Troy, but the old style YHMs are a little blocky…. But they both seem to work well. You can order the old style from Brownells since they are under the $100 ITAR max but the new style are over unless you get the wholesale price.
The ARMS 40 that I have works well, but it doesn’t fold as flat as the others.
The Wilson is a little blocky and square, but it is rugged almost to the point of being bulletproof…. Nothing is going to knock it off and it folds low. I got mine from Brownells last decade…. now they are over the $100 ITAR max they are hard to import.