Torsen diffs get progressively stiffer the higher the difference in output speeds gets. (at least full-size ones one big cars)
A mate of mine who builds them for Porsches explained it to me once and I got a nosebleed halfway through the explanation....
Not actually sure you could build a torsen diff small enough to go into a 1/10 scale buggy without making it too big/thick, which would entail bigger drawbacks than could be compensated by the advantage.
Geared diffs would get a right kicking in a buggy...