What's the (?) difference is this stuff and the kind of SPRAY UNDERCOATING that is paintable. Two types of undercoating, one you can paint, the other is asphalt base, not paintable.
There was a commercial product available in bulk by the trade name BODY SHOOTZ.
Used the similar product from Home Depot on a leaking gutter joint last fall. It was very thin and needed lots of coats. Arrived home this spring to find the joint leaking again. Or possibly even still.
I have recently tried it, It appears to be working, but I used it to seal some electrical connections, Hopefully it will be several years before I find out how well it works.
Home was where I park it. but alas the. 2005 Damon Intruder 377 Alas declared a total loss after a semi "nicked" it. Still have the radios Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times
The stuff "seen on TV" is usually something which has been around forever with a new spin on marketing. That "new" spray sealant is the same stuff you've been able to buy for evaporative coolers for years. Its just a rubberized aerosol spray. I'm sure it works just fine, depending on what you want it to do. I just wouldn't buy the 500 cans you'd need to seal your screen door on the bottom of your boat. Buy a better boat.
I used it on a garden fountain that was leaking and two years later it still holds water. I have seen it for sale at Bed Bath and Beyond,Walgreens and I think Lowes.