I purchased 2 yubikey devices in May I purchased 2 yubikey devices in May, paid for express delivery, and still waiting for the devices to arrive at mine. I have tried to contact them via tweeter and emails but no headway so far

Their product didn't work Their product didn't work. Customer service offered a partial refund (excluding shipping costs). That's unheard of. When a product is returned, all payments are refunded and some will even send the client a free shipping label. When a product is faulty, that's goes without saying.

U2F Keys from Yubico I think having this type of security (U2F Key) and replacing other methods is just excellent. Combined with a password manager like Dashlane for example is just top notch and definitely safe from attacks. It's an open authentication standard that enables internet users to securely access any number of online services with one single security key instantly and with no drivers or client software needed. They come in many sizes fit to the users needs, obviously make sure to have a few spare.

Absolute disaster Absolute disaster. Stay away. No customer service. Yubikey does not work well with Google Chrome and windows 10. I was locked out of all three of my crypto trading accounts after the first day with an error message on all three that said my device was not recognized by windows Chrome security and to try another key.

Using Yubikey introduces the risk of the rightful owner of account is prevented access. It is a problem that Yubikeys cannot be duplicated for backup. They are so secure that even the owner of an account can be locked out, lol. That's not good. In case of lost key or hardware malfunction there is no way to access your account. Unfortunatly two different keys often cannot be registered for the same access. Using Yubikey introduces the risk of the rightful owner of account is prevented access.