used the 21g quite a lot on field based clay shoots - but started to notice a variation between individual cartridges - some were louder than others out of the same box - but this was when there were no other guns about at a dedicated clay ground. The caddy also noticed it and was surprised that some clays were being missed when they were hit the pair before - so they are cheap, popular among shooters and I do like them but I've bought a few slabs of Power Blue 28g they are nice and recoil is minimal.
Oxford Gun Company - where I go mostly at present £35 for 100 sporting, two couses blue and red, red harder on the skeet layout, changes monthly but each covered stand has several options, all guided lovely spot.