One of the shops I go to has one set up on a bow so that people can try out releases. It certainly protects the bow, but in general I don' t like the way it feels when releasing. It' s very bouncy as the air inside the tube compresses and expands aganst the spring/piston pressue.

I guess it would work well for working on your release, but working on your follow-through would be difficult with all of the back and forth motion it imparts on the bow.