Is it too late to start using Firecracker? What if I am done with M1?

It is never too late to get crackin! If you have already been in medical school for one year or longer, you can use Firecracker to catch up on what you have learned, and simultaneously prepare for your next year and the USMLE: http://blog.firecracker.me/students/substantiated-summer-study-strategies-for-success

Winter and summer breaks tend to be very popular times to pick up Firecracker, but the ideal time to start with our program is at the beginning of medical school. If you're already in crunch time with only a month or two left before your board exam date, then here is a guide on how to make the most of Firecracker in a condensed timeframe: http://blog.firecracker.me/students/how-this-crunch-time-firecracker-scored-a-274-on-usmle-step-1