I am not sure that American FIKI certification is particularly relevant in the legal sense in Europe.
The FAA definition of FIKI has varied over the years, and European weather forecasting services do not map onto the American ones. For example, the "throw in everything including the kitchen sink" UK Form 215 forecasts moderate icing in all cloud irrespective of temperature. This makes a mockery of any concept of a departure into "known icing".
(Those correctly dedicated to aviation should now google for "known icing", and read 10 years of Usenet's finest contributions in rec.aviation.ifr etc
).
And once you are airborne, everything is within the scope of "Captain's decisionmaking", including what precisely you do about any given degree or type of ice accretion.
I have found the prop-only TKS system to be excellent, and at something like £3k it is far and away the best 3k one could spend on a plane. The prop never gets iced up, and neither does the windscreen which has remained clear even with 30mm of ice on the wing leading edges and rather more on the elevator (an encounter which developed in stratus cloud in about 5 mins) and I let it go that far only because the surface temp was +3C so providing an escape route.
CAV Aerospace is an exceedingly arrogant company which apart from being hard to deal with has an
outrageous minimum invoice value of £250 so buying any small spares is going to cost you that much at least.