If you are talking about the Teague or Briley thin wall interchangeable chokes, I have had several done by Teague and they were brilliant, and I thought very reasonably priced, but it does involve reproof in the UK which can be a risky business nowadays. Really can barely tell they are there once fitted other than the line round the muzzle face.
They do also offer fixed chokes which are cheaper since you aren't buying a set but then you are stuck with the choice you make.
You will need good thick walls at the muzzle, I have had them decline a couple as they felt there simply wasn't enough metal to do the machining.
I have never had Briley do any for me but I have seen one that was done to a gun I sold, allegedly done by Brilay, and I was rather unimpressed: big recess at the back of the choke tube. But then there are no proof issues.
