Angels have the Phone Box
The UEFI feature is usually disabled in the BIOS.
As @You says, the best thing is to disable it only when you need to use the stick.
Also, it's interesting to note, that starting with W10, MS have made the UEFI disable function "optional", so that the OEMs will not have to provide it on future systems which come with W10 pre-intalled. So, if your FixmeStick is not updated to support UEFI, it will likely become obsolete. This will also be a problem for people who like to dual-boot with other operating systems which don't support UEFI (Linux comes to mind).