The Prometheus Bridge Hop Up Tensioner is designed to be a practical drop in bridge hop nub similar to the old PCS, SCS, and Madbull Fishbone nubs. It comes with both a Purple/Blue soft tensioner piece and a black harder tensioner. Some setups prefer a bridge style setup which forms a concave pressure around the BB as opposed to a top down flat approach.
Prometheus is one of the top upgrade companies known for their high end barrels and hop up upgrades. Based out of Japan they've been releasing airsoft upgrade parts for over a decade and are a tried and true name.