All of this is the most thorough way

You will be required to show the printed letter at arrival and departure

I’ve never heard anything about legal issues. Like I said, I use it all the time, pretty much every month

I used OnwardTicket for my entry into Vietnam back in May and almost every other country. I always buy it on the way to the airport just in case, it’s a small fee to save the headache at the check in counter. I’ve never encountered any issues