For the longest time I've wanted to buy one. I remember wanting to buy one from a reputable source because of all these LioN batteries in the market. A car wants a lot of amperage and no-name imports are just a hazard waiting to happen. Insufficient/fake gauge wiring + bad soldering + possibly discarded batteries by manufacturers being reused to mixed into 'good' battery packs is just plain dangerous when trying to start a car.
The 1st sign was roughly 2012 when Craftsman/DieHard advertised their LioN portable car battery jumper. They never released it. Next thing I know the same plastic casing was being used by no-name import for their battery jumper. I then though about waiting for the major battery tool names (DeWalt, Milwakee, etc) to come out with one. They came out with car tire compressors, but they have yet never came out with a portable car jumper. Kinda hints that perhaps they want to avoid getting sued since it may not be easy to realistically do.
If I were to buy or suggest then I would get something from Anker or Aukey. Both imports, but at least the quality of their other products is decent.