My Backup Pro Online backup

Where exactly does My Backup Pro store your backups online? And it's free, right?
Yeah, but you'll be better off saving them to the SD card. I used to do online backups, bu then one day I couldn't get data access on the road to recover the apps. Obviously no WiFi. I swore to never use online backups again.

Where are they stored? I think on their servers. I could be wrong. I never tried recovering using the PIN they sent me.