I've got two.
The grip can be changed with help from a mill and a doner grip. One of mine has a Phantom(M16) grip and the other has a 45 frame.
Both have D/F bottomlines. You'll get shootdown on CO2 above 8bps, but on HPA it'll keep up just fine. The regulator is internally the same as the RG-1. As long as you keep it lubed, it'll run forever.
I've messed with porting the reg passages and some other internal work but if you run HPA it isn't necessary.
With work you can set them up to shoot pretty dang fast. If you do, look for an early Bruiser powerfeed (or a VM powerfeed).
The stock trigger is indeed a bit of a bear, but there is hope:
1) Polish the plunger portion(part that goes into the valve block) the smoother the better.
2) Shoot the heck out of it. They break in pretty well.
3) Once the trigger is well broken in, you can substitute a softer spring and add a spacer to lighten and shorten the pull.
Neat little guns all things considered. Fairly efficient, plenty fast, with a decent aftermarket barrel just as accurate as anything out there. On top of that, with a little work you have a nearly unrecognizable gun that'll stump the local hero.......gotta love that!