Yeah, the TF I've got is very blue compared to the TK20. I really didn't notice it much before but I was surprised by how noticeable it is in the photos. Really, it doesn't make much difference in most cases; Like I said I've used both for running at night and they both do fine. I do notice that things to me appear a little bit "fuzzy" with the blue light of the TF.
I'd say the reasons to get the TK20 instead of the TF would be only if you want/need something smaller, lighter, and more robust, and don't mind the shorter runtime on high.
The TF is still a great bargain light for ~30 bucks that puts out a TON of light for the cost!
A little side story...
I guess I'd gotten used to the TF and my other bright lights. I was talking to a guy at work who also runs and I mentioned how I would run at night with a light. I showed him the TF and was talking about the pros and cons. He was looking it over and found the switch on the end, and turned it on. Fortunately it was pointed at the wall and not his eyes! :laughing: He said something like "Holy cow that's bright!" and shined it around the walls and ceiling. I'd forgotten how that when most people hear "led light" they think of the 5mm low power stuff, and aren't expecting such brightness out of that one little led!