You'd be hard pushed to find a company with such a good reputation that E-Maps enjoys,a reputation that is richly deserved.
I've used Simon (owner - E-Maps) twice now,both times on 335D's.
Results were outstanding,and the claimed increases in BHP/Torque were exactly in line with what Simon had told me to expect,verified on Dyno days organised on the forum at Surrey Rolling Road.
You'll find many members on here who've used E-Maps over the years,and who would no doubt also give glowing feedback.
You could always pop over to BMWland,where you'll also get the same response from dozens of other pleased BMW owners.