There should be answers. Perhaps your post slipped through the net.
Anyway, for what it is worth. I have no definite answer to yor question, except that it is not a true statement from Macrium.
I use , for my backups, an Acronis USB plug or, as an alternative, a similar plug made with Macrium.
Both will autoboot, if I have them selected in the Bios. My preferred method, though, is to invoke the sub start up menu, available in most machines. The method can vary slightly as:
Start the computer and press ESC, F1, F2, F8 or F10 during the initial startup . In fact, on my Dells, it is F12. You can then select the boot device of your choice.