Sturdy, but a bit stiff mechanically - UTG Pro ACCU-SYNC Top Mounted Deployable Iron Sight

This sight is well-built, and the spring works great. I understand the idea behind locking the sight in the "up" position so it cannot be accidentally knocked down, but it is stiff and awkward to try to push the button and close it. It is also pretty loud opening and shutting. Overall a pretty good sight for the price.