It depends on what you want to use it for. Australia currently has polymer currency that means we've basically forgotten about counterfeiting, but before that we had a $100 note that was greyscale with a bare whiff of colour. Not the best design. You'd occasionally hear stories of people who'd simply photocopy the bill on standard paper, scrunch it up to look used, then find a sleepy clerk at a late night convenience store. Buy a couple of bucks worth of stuff, leave with >$95 real change. You'd have to be pretty inattentive to be fooled by it, but, well, humans have foibles...