I have no experience whatsoever with the TK10, but i do own and carry on duty a TK11. From my understanding, and the fact that my best friend works at fenixstore there are a couple of differences between the two lights. Firstly, and probably most obvious is the fact that the TK11 is black and lacks the clip that is on the TK11. This may or may not be a big deal for you depending on your mode of carry. I personally carry my TK11 on my duty belt in a modified bianchi streamlight stinger holder. Secondly, the TK 11 allows you to use 18650 rechargeable protected LI-Ion batteries which is a huge plus in my book. One other difference between the two lights is the lack of reverse polarity protection on the 11. There are some circuitry differences in the lights as well, but someone more familiar with the lights internals would have to write about that.