I haven't found any useful accessories that take advantage of the picatinney rail mounting point. I created a DIY peep sight with two large washers, separated by an 6" gap, which helps me get on target quickly.
Cons: It came misassembled. The two main barrel parts wirh cross threaded when received. The first look through the lens showed horrible quality. When I reassembled the parts, the image came out quite nice. I dind't think it worth the trouble to send it back.
This review was written in the old system and had content requirements that are different than reviews written today.