And I note that the previously mentioned supplier has a Tru Ball thumb release on the lists for just over ?50... the main criticism I could see for it online is "it's not a Carter", but then it's a third of the price, new...
Note: I've not tried it. My (extremely) limited exposure to release aids is mostly Merlin and Spigarelli. I've played with a Cascade "relax to release" (ugh) version and a Carter chocolate addiction. I got the Merlin because it felt a bit like the Carter, but was significantly cheaper...
But to be honest, my compound shooting is minimal.