i have a similar one .... not the same brand.... works great & like a charm. can jump start a weak battery immediately ... or in another case, totally flat battery (wouldnt even turn the starter) ... i left it attached for 15 mins before cranking (also attached) ... and the engine started no problem!
highly recommend having one (a high quality and safe one, with inline fuse) for emergencies. i bought it initially ... to be able to go out rescue any stranded family member .... ended up using it more myself