I looked at Tuningwerkes when considering the APR route for my Edition 30 but ended up going with Superchips.
FWIW whilst I was being 'indecisive' Reuben at Tuningwerkes was superb in answering my questions and explaining everything. In that respect at least I was impressed by his manner and knowledge.They are based in Croydon so not far from you.
JKM have a superb reputation by are quite a lot further away. They do, however, have a rolling road whereas Tuningwerkes don't.