For me, that Z80 and the ability to experiment CP/M became the whole point of owning the C128 in 1985. By '86 I'd moved on to a Kaypro 1 (which I wrote my first and last bit of assembler for: to drive a daisywheel printer), and later started building XT clones (running DR-DOS, of course).
Unfortunately, the DCR is missing its keyboard :(
It was always a bit awkward with the far reach for accessing the Action Replay cartridge’s (a freezer/turbo-loader) buttons since the cartridge port was way behind the monitor (or in my case, a small TV)
Almost never used any of them other than in C64 mode. Booted CP/M like once. What a waste, all those poor Z80s must be the least utilized cpus ever.