Hey Hal,
The Main Concept plugin packs are for transcoding your footage to other formats (like WMV) from within Sony’s XDCAM Browser app. You only need to buy this if you need/want this functionality inside your XDCAM Browser app, it’s not required for regular functionality with FCP which work’s perfectly happily with the native capture files when wrapped in a Quicktime Movie container. As Craig notes, you don’t need any other app other than Sony’s free XDCAM Transfer (or their free XDCAM Browser app) to handle that simple rewrap on import procedure.
XDCAM Transfer is rock solid, been using it without issue since somewhere around version 0.5. The newer XDCAM Browser, seems no less reliable.
Cheers
Andy