UBI, if implemented, would move O($10T/year) around the economy.
We've seen a lot of small scale studies, which basically boil down to giving people money == life improvements. However, I do not see how a small scale study could possibly answer the open macro questions, like inflationary collapse (e.g. increased velocity without direct economic output), even if the whole "will people work anymore" question is moot.
Without answering those questions, it would be a USSR scale experiment, which is incredibly dangerous. Improving peoples lives would be great, but I cannot see how one could be an advocate for UBI without having solid answers to those questions.