Quite good, excellent value for money, especially if you get them on sale
I got the smaller 37wh capacity models, and one of the larger 73wh models on a good sale
I used one in lieu of a battery resurrecting an abandoned 3.0 Vulcan Taurus, and a 5+ year unstarted 4.6 Northstar Eldorado
Apparently, you aren't supposed to do that, it was never really the same after
They sent me a replacement no charge, and said don't do that again
I don't feel bad about it though, all 5 people in my office bought one after they saw what it could do
While being much lighter and temperature resistant than the old fashioned bigger and heavier lead acid jump boxes
It also doubles as a power bank, so you can keep your phone or hotspot charged in a car without constant idling, or if the powers out at home
Will it start an old 7.3 in an Alaskan blizzard, I doubt it
But the first big snow we had here a few weeks back, wind chill took it near 0, and I got a half dozen miscellaneous cars (Civic/Patriot/Rav4) back up and running, with little struggle
At ~$30, it's cheaper than a roadside assistance call, and you can do it yourself, now, without involving other incompetent people with jumper cables (ask me how I know)
Project Farm did some recent testing, and his findings align with mine, excellent value for money