I bought a USB endoscope from Amazon for about $20 around the time I first bought the boat. Like you, I thought it was a no brainer to have one on board, but I can't say it's been invaluable.
The main problem is that it's hard to position, on all axes. Commonly you get it too close and can't see squat, and the image is often upside down - both of these can be surprisingly hard to correct; the cable is thick, so you twist the stick to get the image the right way up, then look away the screen
and, in that moment of carelessness, it untwists itself back upside down.
Often I find it more useful to use my phone
to take a photo
of an inaccessible place.