I bought one of these tools from ebay a number of years ago because they were quite inexpensive and I thought would be quite useful around the home or for working on the car etc.
This tool would allow you to inspect plumbing blockages or see into places that aren't accessible. The tool can be bought with either a soft flexible cable or a semi rigid cable which can be bent but will hold it's shape.
The tool did work nicely with my android phone, at the time, and the camera image displayed nicely on the phone screen. The focus is at about 3 inches away from the camera. The tool comes with 3 tools that clip onto the camera end. One tool is a hook for retrieving something that is inaccessible. Another tool has a angled mirror for looking at features that are at right angles to the inspection camera. the 3rd tool has a small magnet for retrieving small metal items.
So, just a few days ago I wanted to inspect the furnace AC evaporator coil, to see if it was dirty with dust, which would restrict the air flow through the furnace. To inspect the evaporator coil, I would have to pull the coil part way out of the furnace plenum. This unfortunately was not an easy thing to do on my furnace.
So I got my endoscope out and loaded the app onto my old Moto G cell phone and tried to get the inspection camera to work but with no success. :-( The app ran ok on the phone but there was no video from the camera. This particular endoscope is a wifi version, which uses a wifi transmitter to send the video to the android cellphone. The endoscope shows up on your phones wifi and you connect to the wifi, with the password for the endoscope.
I downloaded other endoscope apps but none of them worked either.
My memory then kicked in and I recalled that I did have issues with the wifi on the old Moto G, at times, being able to connect to a wifi hotspot, but not be able to receive any data.
So I got my newer LG cell phone and loaded the endoscope app on it and it worked just fine. I had a very nice video feed on my cellphone from the endoscope camera. :-)