I just have two, if you're doing strictly u2f they are less than $20. I have a nano4 and a neo that I use for u2f, oath tokens, and rsa keys for sign/encrypt/a

I just have two, if you're doing strictly u2f they are less than $20. I have a nano4 and a neo that I use for u2f, oath tokens, and rsa keys for sign/encrypt/auth. It's not the cheapest setup but it's highly functional and about the best account security I could put together. I lost a gmail account for 45 minutes once and decided that would be much worse then the cost of the keys.