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

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.

Yubico's prompt refund I have a higher import duty issue with UPS carrier for an Yubico order and requested them to cancel after 5/6 days. They cancelled and refunded promptly.

Non Existent Customer Service - Also Just Plain Rude Shockingly bad, full-friction customer journey. Customer Service is non-existent for all practical purposes including initial purchase. I wanted to spend 15 minutes buying these security keys - I'm at the end of day 2 now and still haven't made the freaking purchase due to non-existent help from Yubico and their so-called resellers in the UK. The resellers don't actually sell anything, they refer you on to someone else. If you want to get a freaking headache then please go ahead and start your journey with these unhelpful, rude, time-wasting, arrogant people.

UK customers - Beware the artificially high shipping fee I placed an order with Yubico. They charged EUR15 for shipping. My order was delivered by Royal Mail Tracked 24 service. According to the Royal Mail website, this cost Yubico GBP3.30 for an 80g shipment weight as declared on the Royal Mail label. This means Yubico have charged an artificially inflated price for shipping (GBP3.30 is EUR3.75, which is substancially less than EUR15)