I kept all of the emails I had exchanged with Bob Serva of Fusion while trying to get a 40 cal Fusion 2011 to run, for a while. Eventually deleted them because have them around just brought the bile back up.
Sold that gun for the worst loss I've ever taken on a gun and was just glad to be rid of it.
We have used a lot of parts from Fusion over time. Mostly with good results. Never owned one of their guns.