I had one of those that attached to the phone and it worked very well, had a tiny head and the image was clear enough to be useful. It really saved us when a friend crunched up a spark plug ceramic and we needed to make sure all the shards of ceramic were sucked out before removing it. Having a tiny head on the end of an endoscope really makes it that much more versatile. Another consideration is how floppy the camera wire is - the first one I had, that rescued us was a floppy one, but it did it's job. But if you're trying to inspect behind something, then it wouldn't work very well since it would flop.
The other issue with my USB scope was that the connection to a phone or tablet was flaky.
So for my next endoscope I looked for a small head, semi-rigid wire, and built in display.
I now have this one and like it very much - so far used for pumbing instead of automotive, but it's much better than the USB phone style, and still inexpensive.
DEPSTECH Industrial Endoscope, 5.5mm 1080P HD Digital Borescope Inspection Camera 4.3 Inch LCD Screen IP67 Waterproof Snake Camera with 6 LED Lights, 16.5FT Semi-Rigid Cable,32GB Card and Tools-Orange: Amazon.com: Industrial & Scientific
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There are newer versions of the 5.5mm endoscope, but now they have an even smaller wi-fi version which I would try - it's also semi-rigid.
Wireless Endoscope, DEPSTECH 3.9mm Super Slim borescope for Automotive Inspection, 1080p HD Snake Camera with Light, Flexible Waterproof Inspection Camera for iPhone, Android & Tablet-4.92FT: Amazon.com: Industrial & Scientific
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Amazon.com: DEPSTECH Wireless Endoscope, Upgrade 3.9mm Tiny Borescope, 1080P HD Inspection Camera with IP67 Waterproof Semi-Rigid Snake Camera Cable for iPhone, Android & Tablet-11.5FT : Industrial & Scientific
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I'm tempted to get one with a side-view too - also small, 5mm camera diameter
DEPSTECH 0.197inch Wireless Endoscope,1080P Dual Lens Borescope Inspection Camera with Light,2.0 Megapixels Snake Camera with Flexible Semi-Rigid Cable for iPhone & Android-16.5FT: Amazon.com: Industrial & Scientific
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