I'd say "be carefull"!
I got a NW-MS7 as a present and IMO it's useless. First the memory sticks are rather expensive, and second it is totally dependent on that OpenMG software, which means you *have* to convert your .wav and .mp3 in Sony's ATRAC format before uploading to the player. I don't know if this is still the case for the later NW-MS devices, but please check a review or two and do a search on groups.google.com before buying.