I don't get it, what are people finding so complicated?
It's been in the news for ages now, can't see how people missed it. I tried out the process on launch day, it was dead easy.
The only issue I can see was if I was hiring a car mid-way into a holiday i.e. more than 3 days after departure; when for some it could be difficult to get online to generate the code. I can't see why they couldn't have made the expiry of the one-time code longer, maybe have allowed the user to choose the expiry - leave the default at 3 days, but allow up to say two weeks.