I have R&R over a thousand cyl. heads myself so Yes when I am ready to do my Valve Job I will remove & replace the head myself and allow a machine shop that does Mercedes heads all day long do my machine work. Now I am willing to take on the responseability of possable head gasket leaks, tweaking the head, or any of the many other things that can go wrong on the removal & installation of the cyl. head, you have to ask yourself, Am I a good enough mechanic to rip into the top end of a Mercedes and know all the little tricks so as not to screw up a perfectly good valve job? If yes, go for it. If "well I think so" then you'd be better off with the warranty for the Valve job including the installation. I think my machine shop gets about $1200, complete, not bad. They also replace all exhaust valves regardless, and head bolts.
I do all work on my cars, truck,and motorcycle. But I was also a mechanic for 15 years. Even with the experiance I have eaten a few jobs, somtimes dodey just happens, then it's nice to have a warranty!