for a long time many have said Zgemma are fussy with usb's, I dont find this to be true as I have flashed so many boxes with so many usb's (zgemma & others), while the odd usb may not work 99% will flash once prepared properly (low level format before fat32 windows format), even usb sticks that once flashed & no longer will can be made to flash again IF prepared correctly from scratch. Many have problems getting a usb stick into a state that the box can read from it & then wrongly assume the usb or box are dead/faulty... they will be perfectly fine once flashed.
The need to low level format a usb only applies to USED usb pen drives... A way round the need to low level format is to buy a NEW usb stick (when new they dont need any low level prep, a simple fat32 format then flash files loading then it should be good to go).
As a tip: IF you intend to flash more than once use a dedicated usb to use just for flashing... buy/find the smallest capcity usb you can 2gb - 4gb are perfect but I have used larger, the reason for using small capacity usb's is because it can take hours to prep larger drives!! (smaller is better for flashing).