I have zero personal experience of the full TKS system but I understand from those that have it that the anti-ice position does have a use, in that it prevents the little holes getting clogged up.
I would question the value of the anti-ice position on the prop-only TKS system. There are no "little holes" to clog up; the smallest orifice is about 2mm diameter.
The thing is that none of these systems, known ice certified or not, are 100%. The full TKS is reported as really really excellent under serious icing conditions and much better than rubber boots. I've met pilots who fly in the most northern bits of Europe with it, all year round. But the fluid won't last for ever, so the name of the game remains the same as always: get into VMC, above or below (above is nicer, you get sunshine and a TB has a cr*p heater
)
The fluid in the prop-only version doesn't last long; only about an hour I think, but no plane wants to hang in there collecting ice for that long. A TB20 gives you the option (with an IR) of flight planning a flight at say FL160/170 and that should take you above en-route clouds most of the time. Nevertheless, icing remains a real flight planning issue, all around the year, if one has to go up/down through it. You could get a TB21 (cert ceiling 25k) but then you end up with a W&B issue due to the size of the oxygen bottle
(work it out; 4 pax, masks not cannulas). If I was doing this properly while working down to a sub-turboprop budget, I would get a TB21 with full TKS.
Funnily enough, a TB20 with full TKS, G-reg is KI cert while an N-reg one isn't (last time I checked). Clearly, they have different ice in the USA
NASA have a good icing course on their site
http://aircrafticing.grc.nasa.gov/courses.html but you've probably seen that one.
This site
http://ows.public.sembach.af.mil/ has nice icing region diagrams under Flight Hazards.
This site
http://pages.unibas.ch/geo/mcr/3d/meteo/ under Animated Soundings gives some forecasts of cloud tops and temps (skew-t).
This site
http://weather.uwyo.edu/upperair/sounding.html under Europe, Skew-T GIF has the actuals but they are usually a bit late to be useful for planning.
This is the standard GFS site
http://www.arl.noaa.gov/ready/cmet.html where you can get, among a pile of other stuff, variation of temp (at a given millibar level) with time.
Of course none of this data is CAA compliant; they like you to use the Met Office faxback facility...........