I have no experience w the workshop you mentioned.
Coincidentally, I also go to the Sg Ara area, but to another workshop, M1, a Beemer specialist.
I have been going there ever since getting my car a few years ago; I suppose you can count me as a loyal and regular customer there. The three owners, Jeffrey, KC, and Raymond are all very helpful and passionate about beemers.
If you go there, tell them Lee, blue e36, sent you. They know I'm VERY particular, and if my friends are not satisfied w anything, I'll complain to them.
M1 is definitely not the cheapest place in town. But they suit me fine. I've also tried other workshops to save money, but ended up sending it back to M1 to get the job properly done, always a case of penny wise pound foolish.
I find the trick is to locate a workshop w good credentials, and build a rapport w the sifus there. As they understand your needs and style of car maintenance, they can serve you better and more cost-effectively. If they continue to overcharge and underserve you, best find another workshop.