What always seems to happen with UBI studies is the proponents point to results that say "the people we gave free money to are happier" but never try to quantify whether that money would have done more good used in a different way.
This question is insufficient, because, in most large economies, taxation is insufficient to fund a UBI have any reasonable size. Therefore, new money creation (a.k.a. inflation) is the means, and the timeframe for its ruinous effects are too long to study within a single generation.
That's a false premise. One of the intended effects of UBI is to universalize the kind of stability of cash flow that the wealthy tend to benefit from under Capitalism. This effectively shifts the balance of both economic and political leverage. In the same way that universal healthcare is less expensive than a balkanized insurance system because the people who want lower prices suddenly have a larger say in the marketplace, UBI would lower the amount of capital wealthy individuals and entities have to put towards assets, and raise the amount that, collectively, a much larger number of UBI recipients have.
Under these conditions, it makes a lot less sense to, say, build luxury housing units that are bid up and up by the demand of wealthy investors, compared to seeing that that demand has now been broken up and distributed among lower income would-be buyers and renters and realizing that a lot of money could be made expanding the housing base.
It's all about who has the money. Asset prices will fall as wealth is diffused among people who don't stockpile capital, making the amount of income necessary to survive lower.
Taxation is a cornerstone of making UBI work. Of course it has a higher chance of failure if it's predicated on grabbing money out of thin air.
That all depends on who gets a UBI payment. If it served to "top up" people to a minimum income level, then those receiving the payments would by definition have been paying little enough tax that it wouldn't have covered the UBI they receive. So in those case, yes, they're probably more happy to receive the UBI than to have the tax waived. UBI doesn't require it to avoid means-testing the benefits, it simply sets a minimum acceptable income and lifts anyone below it up to that level. People with high incomes pay for it.
Typical UBI proposals are "means tested" in the form of a "negative" income tax (NIT), or as we call it nowadays, a refundable tax credit. If you make 0 taxable income, you get a "full" UBI payment. Then some percentage of your earned income (typically 60% or so) is clawed back from the UBI, until the break even point is reached where you get nothing as UBI, but also no further earned income is clawed back. This gives acceptable work incentives at the low end, very good ones above the break-even point, and a low monetary cost for the program as a whole. It is important that the break even point not be too high, or the cost of the program would be way too high for little benefit.
It will disincentivize work to some extent, among a comparative minority of UBI recipients. But the flip side is that by keeping the break-even point at a reasonable level and not pushing it too high, you actively slash costs for the program as a whole. The effect of having moderately-high clawbacks at the low end ripples upward, saving a comparable disincentive for every income above the breakeven point. This is a key insight about non-linear income taxation which is borne out by computer modeling of the "optimal" (utility-maximizing) tax rate structure, and economists who are knowledgeable about the subject do agree on this. It's not really controversial.
