You've got a half dozen old guitar straps lying around and you're wondering if you need a banjo strap. You do - you can attach a guitar strap to a banjo, but it's a fiddle. Just get a banjo strap and clip it on there.
You're wondering whether this, the cheapest available banjo strap, is okay. It is. Go ahead. Your banjo playing will not be improved by paying twice as much for a strap.