The real issue with UBI is what it does to an economy when *everybody* has it.
Not really. We essentially have all of the bad parts of UBI in the US with none of the good parts. The results are poor, for that reason.
The way our public assistance works, you need to make less than $X to get the benefit. If you make $X+$1, you don't get the benefit. That's a huge disincentive to work.
UBI works differently. You get your UBI, period. It is totally separate from the money you make ($X). Now, if you make more than $X, your taxes on the $X+ go up. The further from $X you are, the more your taxes on it are, but they never are more than about 50% a the very top.
Throwing imaginary numbers into this, if I get my $2000 per month UBI and I make another $1000, that $1000 gets taxed for $250. I'm now at $2750 for the month. If I get my $2000 UBI and I make $10,000 that month, and I get taxed $5000 on that, I'm still at $7000 for the moth. It's never not worth making more money with UBI, they way it is worth not making more with food stamps, Medicaid, etc. With these current programs, you make too much and you're cut off. Often before you have the financial security to be able to make it on your own.
Where I think UBI is going to shine is that it's going to allow the creative types to try to make money doing what they love. More arts, more stuff being made, more food carts, gardeners, bee keepers, and microbreweries. Right now, these are very tough professions to make a living in. If people didn't need to make a living, many would do what they are passionate about, not just grind out 40 hrs. And all the folks sitting on their ass collecting the UBI will have the money to spend on those things. And that means more taxes collected, which funds UBI.