Just tried this today and it worked really well.
I have a KTM 990 Adventure and filling up its dual tanks is always a hassle. Its easy to have gas spray back if you don't get the correct combination of nozzle angle/gas flow and vapor boot pull back.
The tool was easy to slip on and gave plenty of visibility when fueling up, especially since I now can now do it one handed.
I keep the tool in my glove box. Well worth 5 bucks.
A metal version might be nice.