Generally it's safe to do but if you have any concerns its best to contact MOTU. I own the MK II and had no issues updating that. The recovery procedure (in case the update goes sour) usually involves rebooting into the update mode and running the installer again. On the MK II you can also do the reset to factory and that also takes care of the quirks (if any introduce themselves after the update process)

...But just so you know the chances of the actual update process going sour are as slim as the chances of you getting struck by lightning. I mean shit does happen. Just not all the time and definitely not to everyone.

cheers,