The DD is too big IMHO and also far too expensive. So best would be to have a ZIP drive. You can hook it up to your PC if you wanna store ROMs on a disk to play them on your DX2. You can copy any game cart "fast and easily" to any ZIP disk.
Again unfortunately, the old ZIP drives required for use with the DX2 are hard to find these days (maybe I should try and get one via eBay)...
So, I agree concerning the DD. Best solution is a ZIP drive, I'm persuaded about that.
-Cyan