It seems to me that every basic income ‘experiment’ is flawed because they don’t account for the externalities of higher taxes and the fact that the pool of recipients is limited enough that the market is unaffected. Giving a few thousand people a few thousand a month isn’t going to cause much on an impact on inflation and it’s not going to make rents go up across the market. Additionally, others outside the experime…
Most importantly, they're connected. As you noted, of course people are happy to get "free" money. But what happens when the markets eats up that extra and they are back to normal, or perhaps worse off? Happiness isn't going to stay high.
In theory, I like the idea of UBI but I'm also confident the market (at least in the USA) - specifically housing - is going to quickly eat up anything extra.