I have a Emitech K950X (EMS 950X in the US) with their FTM. I use the FTM in a passive mode, i.e not controlling the deposition. Perhaps it is not the worlds most sophisticated FTM either, but...
I remove the crystal from the holder and carefully scrape the accumulated debris off the crystal with razor blade. I have been doing this for at least 10 years.
I can't comment on the accuracy of my FTM, (other than by occasionally coating a piece of brass) but my reproducibility hasn't changed much in 10 years - given some care and a reproducible setup (rod diameter and length, number of deposition pulses, pulse length, spring tension, position of rods, etc) my FTM returns 20nm +/- 1nm 90% of the time; larger deviation is usually associated with sloppy rod preparation and inaccurate rod positioning.
Gareth