gee 4th i have no first hand experience with that product.
i don't see why it would need a mil-spec buffer tube as the assembly just sort of jumps back and fro in the stock giving the simulated auto effect?? it is just a slightly larger and thicker tube--nothing majic-jack about the mill tube.
$200 sounds fair to me. i figure it most likely works there is just some assembly bug that prevents its full function.