DEPSTECH Wireless Endoscope, IP67 Waterproof WiFi Borescope Inspection 2.0 Megapixels HD Snake Camera for Android and iOS Smartphone, iPhone, Samsung, Tablet -Black(11.5FT) Just bought one off Amazon with a 20% off coupon, now down to 5%. Will be nice for working on car and things around the house where it is difficult to get a good sightline on where you are working.
Not sure if they are a fad for exercising or not, but I do see them in use by quite few a people in the fields of exercise science. Our youngest used them for awhile to rehab a hip injury when he was in high school, and it did seem to be beneficial.