USB is not good for writing Atari floppy images. And it is same under any OS. Even formatting floppy on Atari to 800KB will not help - because writing will just skip 10-th sector on tracks, so you will get unusable floppy, with missing parts.
I think that cheapest way (but needs some space) is using some old(er) PC, with built in floppy drive. Then you may perform disk image writings properly and fast.
What kind of PC ? Something what can run XP, so even Celeron, K6 based (400 MHz) is good, with 128-256MB. But for instance even miracle is possible with very old 486, P1 system and WIndows 95 : it can handle directly 800K floppies and will recognise even those formatted under TOS 1.00 . On such may run MAKEDISK for writing image files.
Some more info: http://forum.8bitchip.info/faq/