It stores it's image backups in files with the suffix. Unless you do this you can never be sure that when you need to restore a backup you'll be successful.

The best way to do this is to create a backup image of a hard or solid state drive and then restore it to another similar freshly formatted drive and confirm both that the PC boots from the second drive and that all your software and files are present. The most important thing with backups is to test the recovery process works. If you want to use the software that is quickest then Acronis, when running from either the bootable CD or the installed program, is usually faster than Macrium both for backing up and restoring. In my opinion if you just need the software to do backups and nothing else then Macrium is much simpler and of course cheaper (for the free version).

I use Macrium primarily for live imaging from within the running Windows and Acronis for 'cold' imaging from the Acronis bootable CD. I've used both Acronis and Macrium Free for many years with 100% reliability for both programs. To answer your question as to which might suit you best.

Macrium reflect free edition review