However, a higher velocity of capital without commensurate economic value being created ~= massive inflation.
This is a potential risk for UBI, and one that small-scale studies do not cover. Ideally, the additional economic value would be greater than the face value of the capital transferred every year, but there is no guarantee that is correct (nor is there any reason they should even be on the same order of magnitude).
Implementing UBI on a national scale would be a grand experiment. Most grand experiments tend to fail with massive upheaval. I think for UBI to be adopted, you would need a plausible incremental strategy with a lot of safety checks.