If it works as advertised it should be fine.
I use the CTEK 800 (smaller) and with the car off / lights off just accessory on (check engine light) I have been fine. Once you are setup to flash it takes about 30-60 seconds. Only real reason you need a charger is if you get an error on the software and you have to figure it out which adds to the time.
Just remember to take your time