While JV-1080 is a professional sound module and used by a lot of composers in professional recordings, it likely wasn't used specifically for General MIDI composing. Reason being is that the SC-55 and other more consumer level devices were what people were more likely to actually have, therefore it made more sense to compose General MIDI tracks with those devices.
There is also a big issue with the JV line of synths when used for GM playback. If too many program changes occur at the same time as musical note playback, it causes a delay in the playback of the notes.
While I don't have a JV-1080, I do have a JV-1010 (which has both JV-1080 and 2080 samples) and this issue is noticeable on various soundtracks. And I have read that this issue is present on the JV-1080 as well. It's also present on the later XV-series of modules, albeit the delay is much shorter.
This issue does unfortunately mar what otherwise could be one of the best GM playback devices. The particular Roland GM samples used in the JV-1010 is among my favorite in all sound modules.
The other thing to be aware of is the JV-1080 is kinda big compared to desktop sound modules. While it can be sat upon a desk, it's really designed to mounted in a 19" rack. Smaller desktop modules are much more convenient.
If you can get this particular JV-1080 for cheap, you could always try it out. If you didn't like it, it would readily resell.
On the other hand, if you're looking for a sound module that is more suited to General MIDI playback, nothing beats the SC-55 (and variants).