I have a "Depstech" (Derptech? Something like that) one that's been pretty handy.
Their phone app is dreadful, but mostly sort of worked. However, I discovered almost by accident that it worked without any added software on my cheapo Chromebook. It has a weird USB plug that works as both mini USB and has a little flippy part that makes it full-size USB.
I just plugged it in on a whim to see what happened, and my Chromebook saw it as another camera. The larger screen makes it a lot handier.
For the miniscule amount of money, it's super-handy.
You can't see sideways unless you have room to bend, and the first inch or so doesn't bend.
So if you stick it into a spark plug hole you can't see much of the cylinder wall and it can't look backwards to see the valves. I've seen mirror attachments that might address that, but I haven't really pursued it.