Are they the best in the business? Should I be paying them a visit?
Province: Krung Thep
Suggest you use Raja's or Rajawongse they are probably the most reliable in the midrange price scale - for best in class try Art's Tailor - but they are very expensive - I guess you get what you pay for.
There are many good ones in Bkk as there are many bad ones as well. Be careful of newcomers in this business. With "Needleking" on Sukumvit Rd I have good experiences over many years.