i used a usb to paralell cable with my gerber edge and flexisign.. can't speak for every brand.. it worked pretty ok... but
there was alot of weird errors, incase i managed to print with the printer offline and got an error message from the gerber edge i had to restart the whole computer
the printing was taking sometimes 1-2 minutes before it started, and could freeze for 1-3 minutes in the middle of a print and sometimes it never started just stood there and nothing happenend...
i got a pci paralellport card and it was like day an night, printing speeded up alot and no wierd errors ever again as on usb..
sometimes when i rebooted the computer the usb port -> paralell port had changed number so had to double check everytime that it was still correct...
different computers, different windows revisions, different flexisigns, different usb cables, etc etc tons of things that could make a difference
i would recommend getting a pci/pcie card with a paralellport incase its possible, its usually cheaper then a usb -> paralell... and incase you experience wierd problems with your usb cable... skipping the cable might be a solution and go with a card..
i even had tons of problems sending via a usb-> serial port cable quite often it did not cut the whole piece if i had like 40 stickers sometimes it skipped here and there and in the end it was like 25-40 that was cut..
then again i did not use the gsp recommended cables. and did not use omega.. so can't curse them all but in my configuration usb->serial and usb-> paralell did not work so good, tried it on 2 different computers...