I have used this before but found multiple incompatibilities.
The idea of changing the user agent to match something else is pretty good, never thought of that.
Of course it's possible to do that by other means, but this addon does throw up some pretty funny combinations.
I remember when I used it at my old school on portable FF it threw up "Mozzarella ThunderMonkey" which my teacher thought was real. he then went and searched it on Google and apparently the results were . . . interesting, to say the least.