Had mine coming up two months now, I can confirm it's very useful. Purchase admittedly half inspired by this thread.
Perhaps obvious, but I can't remember a recent tool purchase that brought me such a completely new and unlike anything else capability.
Water/oil/air leak? Stick this in there while the leaking thing is operating/flowing. Don't speculatively disassemble things and try to imagine where it might be leaking while it's turned off.
Can feel a fastener or clip but can't figure out how to undo/refit it? Stick this between your fingers and take a look.
Want to identify a part or get its number off the label? Just take a picture with this rather than removing it.
Stuffing a cable/pipe down somewhere, trying to get it out the other end? Use this to check what it's getting stuck on, and to help you fish in the right area at the other end.
Note you have basically zero control with lengths over say 1.5m (5ft). I've read about the technique of putting the camera head through a small ball, to avoid it getting caught on things so easily, and keep it off the surface of pipes. But not tried this yet.
Auto up orientation feature is also very useful. Would be even better if it was possible to manually set which direction was "up". Things get confusing.