Quality is acceptable, but not up to the standard of Hoya HMC or Hama HSMC filters.
Most of their coloured and conversion filters are not dyed in the mass glass (ie: the glass is coloured), but are laminate (sandwich) designs like the B+W filters where a gelitine filter is sandwiched between 2 pieces of glass. This is a double edged sword, as in many cases laminate filters degrade over time and thus cause a colour temperature shift. This may not be critical for all but the most demanding professional applications however.
It's also true that Tiffen dominate the Hollywood scene filter wise, but hell, what do you expect? Tiffen is a US company and have targeted the cine-camera market for many decades.