I had a Z3-style M roadster back in 2004-2005 and now have a 2007 M Roadster (Z4-style). Both have been great and problem-free. If you're looking for a roadster, they're not a bad choice, and are among the least "girly looking" of the two-seater convertibles available, for what that's worth.
(Especially the M cars.)
I'm actually considering selling my 2007 in the next two months or so before I transfer for a slightly larger convertible (M3) to enjoy the topless thing and do some traveling with family, too when the Ds are absolutely not right for the gig. I'll be sure to post info on it or send you a note when I get to convincing myself its the right thing to do.