I used aluminum retainers for a time and the only problem I had with them was wear. It was prior to having roller rockers. The stock rockers always "worked" the valves causing wear to the spring retainers and valve guides. I found evidence of this when cutting open the full flow oil filters.
All of it looks great...............Good Luck

216.158 MPH 12-Port 302 GMC on 70% 171.0 MPH 302 stock head on gasoline 7 years later