I have both 8256 and 8512 Amstrad "Joyce" machines and an AMX mouse. The interface slips over the edge connector. The 8256 has twin drives, one of which is double sided. I thought I'd get it out and have a play and I think it is very slow. You can see it updating the screen a character at a time. I mean, you can follow the screen update horizontally with your eyes which is to my mind really terrible. In the UK they are still cheap. I think I paid £15 each, both with printers and disks. The keyboards are awful, I have to say. Very light and plasicy, but usable.
It's probably worth fitting a pair of 800k 3" floppies instead of the horrid Amstard drives, but it really needs a hard drive and a speed boost.
To answer another question, I will use it for development. The M4 already has C compilers installed on its Cheapo IDE widget and I am looking to build a vi clone for it (an early version of stevie which I am going to port to CP/M). Missing keys on the M4 keyboard (tab, escape, [] {} etc) are a pain but as I said I have it connected to a dumb terminal. The worst thing is having to exit source code with WordStar. Slow and awkward for me as I don't know the keystrokes. I can see its a powerful word processor otherwise.
Naturally this version of vi will be released with source and credits, but I have a long way to go yet.