A couple of years ago, I bought one of those small form factor jump starters. It was only okay for me and then eventually, wouldn't work anymore under light use. Then my buddy bought one of these off of the "Snap On Truck". He told the dealer that if he could use it to start a 3/4 ton Avalanche with an 8.1L big block V*, he would buy it without question.
They disconnected the battery, hooked it to the cables and it fired right up... several times! He bought it and said that he has jumped over 3 cars with it in a couple of months and he hasn't had to recharge it yet. I had this in my cart for a while. I wanted it, but did I want it $200.00 worth... I finally decided to get it. The day It came, I charged it up and put it in the case I got for it. The next day, I had to jump my wife's van. The battery was SO dead that the jump starter didn't even recognize that it had been connected to a battery. There is a "Bypass" button on the unit that allows it to work even though it does not see a battery. I clamped the cables to the battery, hit the bypass button, turned the key and it was running... just like that. No waiting, charging, slow dragging engine. It started like it had a brand new battery under the hood.
You can also power a cell phone, tablet or 12 volt accessories with it through the included adapters. This unit is great to have during extended power outages to keep your phone charged up and should you need a jump start, you'll be more than ready with this. Yes. It is expensive but you get what you pay for!