I have the 3/8" version and the first time I really needed it I believe I got my money's worth out of it. Very rounded and very tight starter bolt on a front wheel drive Nissan. BEHIND the starter and access could hardly been worse.
After trying lots of things I got a rounded bolt socket, like one of these-
https://www.northerntool.com/shop/t...Iiiv7lY4L_T0DfSqPECF5p-L6twWwX-xoCRd8QAvD_BwE
and used it with the Mayhew tool and an air hammer. Beat snot out of it which jammed the socket onto the bolt (finally!) and then a regular impact was able to knock the bolt loose.
The Mayhew helps break things loose here and there but isn't so great with regular bits and sockets. Often a hand impact is better for seized screws. You can hammer like nobody's business, but your twisting ability is limited. The vibration throws your wrench out of position too easily. BUT when you have something REALLY stripped and have such rounded bolt sockets that have to "bite into" the fastener to work, the combination is really impressive. So I don't use it much as designed but more to "set" other extraction tools. Not something I use much at all but a truly worthwhile weapon of last resort to have in the back of a drawer.