When has UBI actually every been tried? I don't think any trials really qualify as "Universal". IMO the universal part is the hard part and changes it drastically. Compared to a small limited trial of giving people money, where does it all come from when it's actually universal? And what are the effects on the overall economy when it's universal?
Taxes. One form of UBI is essentially a negative income tax rate for people making below a certain line. As more and more jobs get automated away, we will either become a society of wage slaves with a small upper class controlling trillions (wait a minute...) or we will distribute the benefits of an automated society to all people.
A lot of it is pretty hand-wavy and I'm not sure how legit it is. I'm posting it because they claim it won't cause taxes to increase for the majority of people. Instead, it comes from mainly corporate taxes and other sources.
Of course, it seems likely that this just passes on the cost to ordinary people in the form of increased costs for goods and services. As for inflationary effects, I'm not qualified to say.