I have had 2 of them, one cheap ~30€, another higher priced ~100€. I have to say both were waste of money. Short after buying, they started to loose charge or could not reach the full charge. I used both of them in action, and my opinion is that thay can perform only few decent start attempts (at least with CDI engines).
Nowadays I have Defa and Benton maintenance chargers (Defa for fixed car installation, Benton for temporary other car/battery over night charging) and if I need a jump start, I have two old 100Ah batteries which I connect to car if needed. Conventional starter batteries are cheaper, higher Ah capacity and more reliable than jump packs... I don't need light, air compressor, usb connection or whatever these starters are offering.