I have used my 1000A jump starter at least 20 times (very successfully) in the past year, I recently bought the 2000A unit when I knew I was buying the 7.3L Tremor. Thankfully, it got my Kubota started after the 1000A unit failed several times. I had to bury one of my dogs, it was a cold day and the tractor had been sitting for a few months. No real way to get jumper cables to it due to how and where it's parked. They keep their charge for many months, most of the time they will have the charge you need when you need them... but when you do use them, recharge them to 100% at that time. I've started 3 cars in a single day with my 1000A unit, not sure if I could have done a 4th.
Funny story, but I left my wallet at home one day ... I was running on fumes and a lady had a dead battery at the pumps. I ended up trading her a jump start for $5 so I could get enough gas to get home. Wasn't trying to rip her off, just needed to get home grab my wallet and come back again. No worry about sparks with these units.