They do get used to the beep/thunk. As for training, food/based training / holding the flap open for them the first couple of times has worked well in the past. Shoving them through was less successful. You can take the actual flap out for a couple of hours so they get used to going through the hole, then put the flap in but with the latch permanently open so they get used to the flap, then put the latching on.
As for range, I would have thought if the chip it in the shoulder that would be fine, if not vet should be able to put another one in for £25ish? IIRC correctly they just use a massive needle which is not as bad as it sounds since cats have very soft skin.
If your cat decides it enjoys some kind of catflap standoff taunting intruders stuck outside the catflap, this can backfire as certainly with the Petporte they can trigger the catch from the inside.
If they could combine one with some kind of cat-scarer to deter intruders that would be even better!