The only drawback is I also use an ActionReplay cartridge Mk6.0 in C64 mode and it needs to pulled out every time I go to C128 mode.
I would guess that is because the 128 automatically switches to 64 mode when it detects certain cartridges. The WarpSpeed 128 cartridge had a switch for 64 and 128 mode. I think I still have mine around here with two other WarpSpeed carts (the best fast-loader and utility cart, IMHO) one which supports the 1581 and one which does not.
I love my 128D. Recently got most of my drives and systems JiffyDOS-enabled. Need JD ROMs for my two MSD-2 units, though. Assuming they still work, I haven't had them out in ages
As for the RGB, I used an old PCjr monitor with an adapter I made. Looked pretty nice. My only lament is that back when I programmed these things I didn't take up programming in 128 mode. I was moving on to the Amiga at the time, so the 128 started being neglected. *sigh*
