What everyone has been waiting for: an indepth comparison between these two brushes. Well, maybe not that indepth because I really need to get some stuff done around the house. In a nutshell, though, here it is.
When it comes down to it, I MUCH prefer the Tangle Teezer over the Knot Genie for the following reasons (most important to least important):
1) Effectiveness: I am not sure, but I think that the TT is quicker. That may mostly be because of the second reason, which I am about to list. I feel like I am moving more quickly with the TT, for whatever reason, which means the job is done sooner.
2) Gentleness: I feel that the TT is much gentler. It just works better and slides more easily through the hair. The KG makes sort of an audible pulling sound, that makes me nervous, whereas the TT is quieter as it works it's way through.
3) Shape and size: The TT fits in my hand much more nicely. It is a bit smaller and is contoured to the hand. It's easier to hold as I brush. The KG is somewhat larger and it's a bit wide for my small hands. It does have scallops around the edge but they don't really help me keep my grip.
4) Price: Knot Genie retails for $20 on their website and ships to me for $26. On the other hand, I picked up the Tangle Teezer at Sally's for $10 plus tax.
When using the TT, it has not bothered the girls at all, so far. Today, I got several "ouches" when using the KG. If you feel the bristles on both, you will find that the KG's are much more stiff. I can see that it might out-live the TT, because I am finding that a few of our TT's bristles have become slightly bent from being used again and again. However, I can't imagine the brush completely losing effectiveness from that kind of wear and tear.
I also tried both myself and I actually do like the stiffer feel of the KG. It feels good on my scalp. So I will probably keep using this brush even if the girls don't. I also got the Miracle Detangler which has a REALLY nice scent which I enjoyed. It didn't work better than our usual products, however, and the bottle is tiny.
In closing, I sort of regret spending $30 on the Knot Genie Father's Day sale. I should have just bought a second Tangle Teezer and saved my money. However, BOTH brushes are *vastly* superior to anything else I have seen, particularly for curly headed kiddos. Hope this helps!