Not blaming my tools Robin, forced to use them at numerous other peoples one was an engineering firm who saw fit to replace with R8 collets after.

The nature of what i do i have to be able to frequently change cutters quickly increasing productivity and have accurate grip ie three cutter changes in 2 mins wouldnt be uncommon. Work it out less than 8 secs to change a cutter with R8 or MT2,3 against how long it takes by other means, excluding hydraulic and air types.

Maybe i am spoiled being brought in to milling with an engineering company using R8 collets, if i didnt know any better i would probably be a lemming your loss. I would never own any ER or Clarkson collet setup, why settle for second best, but would invest in the 5C for other purposes if need arised.
Take the Clarkson - Remove nut, find collet and screw in cutter, place collet with cutter in and adjust depth of cutter by rotating in the thread then tighten up nut. I have known them to run out even visually with the cr, the less parts in the setup and distance from original spindle fixing the better! My dislike is they take an eternity to change cutters, same with ER and other similar types along with cutter slipping or dropping. Just by the time the nut is removed i could have in a new collet and cutter fully tightened up.

A good tip while i think of it is make up a spindle lock if not fitted whichever type of rotary clamping system used.

Now i may have figured the source of the ER and CMD cutters slipping and dropping problem with all chinese and proper expensive English and German made examples. The nut binds and theres a limit to how tight the collet will go. You will know this when you have a cutter drop and the nut is tight still!