Same reason I don't, limited quantity. I don't have the numbers, but 2hrs quantity if I remember right, and that's not even on high. Then you also have to carry the stuff around because you're going to who-knows where that doesn't have it. It's expensive to buy at $11.50/gal in a 55gal drum($16/gal if you buy it in small quantities). She's ferrying these planes across the pond, and I'm thinking TKS fluid is on the short list of items fuel stops carry on the way over.

Another thing not to like is they are counting on prop-spray to cover the "pod" and I don't know what they are doing for the windshield. Preferably, a FIKI plane in my eyes has a hot-plate or windshield, I've flown a few alki windshields, and sure they clear the ice, but it's really the lesser of the two evils because you still can't see through the alki if you don't time it right if the ceilings are low. They work great when you have about a 1000+ft ceiling, because it gives it time to clear, but anything less with icing down to the surface is bad!