Keyboards like that are overrated. Although I did like the "Options by IBM" line, it had a short life.
The only reason I have to like the M15 is the dual arrow key setup, that is fricking awesome. Then it would eliminate having to move your left hand all the way to the right and have your hands cramped.
But yeah, I'd only take an M15 if it was free or in the dump or whatever... seeing as I haven't paid anything for any of my six keyboards lol.