I can't comment directly on your question, but I can say that Adobe uses several Main Concept bits in Premiere Pro and that my past experience with Main Concept's plugin has been a good one.
As a reminder, Adobe Premiere Pro CS4 supports XDCAM HD, and EX (35mbit/s) natively without the need for a 3rd party plugin.
Hope this helps,
I have installed the MainConcept XDCAM Plug-in, and can import and fluidly edit .mxf media originating from the Convergent Design nanoFlash. I am expecting delivery of 50-90 minutes of 1080p 23.98 in a few days, and I will report any problems if encountered.