I wanted an adapter for the Stryfe that allowed me to use some PVC pipe for the bulk of the stock. I wanted to match the lines of the Stryfe body as much as possible (the left side wall would have been way too thin, so I built it up a little). Having two pieces to the collar allows for a redesign of just that side.
I don't plan on removing the stock, let alone during games, so semi-permanently clamping it with the screws was favorable to some spring-loaded design. Once screwed together, it's very solid and it's not going anywhere.