yes i beleive others have had success with this method.
mh on the barefoot forum is a big beleiver in the sitz bath.
yes i beleive its good for both kinds, i think mine are mostly internal.
i guess if you do them often enough it would keep them from coming back but as others mentioned while these are 'quick fixes' you still have to find what is causing the problem.
anytime i feel just a little something not right, i do a sitz shower and it clears everything right up.