ONly Professional and above can backup to network shares. The file format is VHD. On a local drive (e.g. USB), I believe the backup routine will manage space, but on a network share it won't. There are a couple of other oddities on drives that aren't NTFS but Microsoft and Wikipediai will have the details.
I'm a long-time Acronis user, but I am using Microsoft Backup and Restore Center on newer machines mainly because it's free. If you have a mix of NTFS and FAT32 drives, Acronis may still be better but I'm just guessing.