I've been using the 2.52 beta for a few days prior to the official announcement and it works really well with WM2003SE. No problems at all.
I'm actually one of those who had previously registered both PocketMusic and then PocketPlayer. I haven't played around with the latest version of PocketMusic (version 3 now?). But back in previous versions, I found PocketPlayer to be more stable and more robust. I would have been willing to give the latest version of PM a try but they're charging an upgrade fee for version 3 (which is what I need to use with WM2003SE) while PocketPlayer was able to get me a WM2003SE version for free.