This has to be the most useful tool for anyone who needs to solder a pipe while the water is still persistently dripping (thus cooling the pipe so it won’t solder properly). Just insert the tool and tighten the end nut to expand the rubber plug and presto, dry and ready to solder! I would imagine it could be used to stop a leak in a broken pipe too but I haven’t tried that one yet (and hope to not have to), my nextdoor neighbor could have used it when he broke off the toilet shut-off valve while trying to “fix” it. I am not a plumber but I do my fair share of plumbing and wonder how I ever did without it.
A cool tool is anything useful that is superior to comparable items. If you think this tool is inferior suggest a better one. You are welcome to insult a tool, but comments containing insults to individual people will be deleted. Corrections of fact are always welcomed, if stated politely. Recommendations of better tools are dearly wanted and may be elevated to the front page.