I had the TKS retrofit carried out here in Germany on my M20K 231 abput two years ago. As stated by others in this thread, this is a non FIKI-install (propably due to the single alternator and 14V electrics of the 231).
Cost was about 35.000 EUR for the kit and 140hrs in labor (about another 14.000 EUR here in Germany).
The cynic in me could now argue, that ~50 AMUs bought me a nice "Flight into known icing conditions prohibited" sticker in plain sight of the pilot. However, I do not regret the installation for a second, because it truly provides peace of mind in terms of dispatch capabilities, i.e. I now depart into weather were icing might be encountered without sweaty palms.
To my surprise, actual use of the system so far was less than I would have expected, i.e. in situations where I would have assumed to encounter icing, actually I didn't.
Speed loss was neglectible. However the TKS puts a substantial burden on useful load (which isn't excessive in a 231 anyways).
Unlike e.g. non-FIKI Cirrus installations the TKS system for the Mooney (maybe the retrofits in general) to my best knowledge is the same as the FIKI-one (i.e. 6 usg/ 2hrs TKS capacity, all surfaces incl. rudder de-iced). The only thing missing is the 2nd pump.
As others pointed out, I'd consider it more sensible to invest in an airplane I know instead of buying another one with FIKI capabilities and unknown quirks. Hence the retrofit instead of looking for a new plane.
In my opinion, a piston powered non-pressurized plane, whether FIKI or not, is not an all-weather type of airplane. I.e. one can push the limits a bit further, however for serious flying in adverse weather, I'd consider a (single engine) turbine instead. I do realize, that Cirrus owners who spent 1mn+ USD on a non-pressurized SEP, might want to argue that :-)
