I got my Tac suit Bats ankle extensions from One Sixth Kit. The definitely make a difference, they're worth it.
I've said this before but will do so again: In my case I don't use crotchgrabbers to display my figures. A word of caution that the extension joints I received were a less snug fit than the stock ankle joints. And even in a fairly conservative, non-dynamic pose, after a couple of months the weight of the figure did not support the bend at one of the ankles and the figure tipped over! I think I can still can find a way to pose him without the crotchgrabber such that he won't eventually tip over because the ankle joint isn't snug enough. But I do have to be careful with it. It may just be the luck of the draw that the joints sent to me were from a batch that were molded with just slightly less width, etc.