I've never owned or driven a Z4M but followed one once . O.K, the full story is I bought a set of wheels, way back in 2011, from a guy who traded his 350Z in for a Z4M and had to follow him from our meeting point back to his house to get the wheels. Got talking to him and in general he was very pleased with it, the only thing that was bugging him was the amount of time it was off the road about 6 weeks in the 4 months he'd owned it. Electrical problems that proved difficult to fix, indeed it was due to go back again with another problem. The car had a dealer warranty so just annoying more than vast expense. I don't know that much about The Z4M, I'm guessing its a complex beast, but I do know that The 2.0 Z4 that Caroline had brand new had to go back to the main BMW dealer in Chester on 4 occasions for warranty fixes my Zed now 8 years old didn't need any warranty work and the only fault it has developed is the clicky axle. In fact in the 70's and 80's I owned no less than 3 Datsun Cherrys and my ex wife owned 2 of them, all brand new and not a single fault with any of them.
Pete