I've got a collection of some 60 historical bugles and trumpets (without pistons). Wen you purchase these old instruments, it's inevitably that a high percentage of these have stuck mouthpieces.
With this instrument, they all came out without any problem.
The only thing is: take your time to position the "teeth" carefully and judisciously and fasten them before you begin to pull.
This is very important because you could otherwise damage the ridge on which the puller is pushing back.
But if you do that carefully, it works like a charm.
Highly recommendable tool !