Useful if you ride in urban areas, as air pumps fitting for schrader valves are plenty because like every car uses them, sclaverand or even dunlop - not so much. Just screws on, fill tyre, go about your way
Are they high quality? Nah, wouldn't really use this in a workshop setting. But to put on your keychain or something in the event you might need it? Pretty good! And they're cheap enough if you find a miserable soul with a slow leak who didn't plan ahead you can just give it to them
I have a plastic version of one of these that I just use as a presta valve cap on one of my wheels. That way it's always handy if I need it, and I just remove it if I don't like a regular valve cap. Might order a handful for my other presta bikes as well. I guess you could even put a schrader valve cap on it if you want extra protection too.
I used to carry a valve converter with me (non-keychain) for my dunlop/woods valve, but ended up purchasing a universal aftermarket pump head for the mini track pump that follows me everywhere.
I run my tyres at 90 psi/5.5 bar and felt a little sketched out using the adapter although tbh there's absolutely nothing wrong with it
