In the article they mention, that people from experimental group (w money) are feeling better from health perspective than people from control group (w/o money). I believe that's a strong point to justify the expenses.

Uh, the very first sentence states that people feel better on UBI, for no loss of employment rate. So basically all the mental suffering associated with unemployment is pointless suffering.

I'm not sure you can deduce that it's pointless. It's not like UBI doesn't have any other consequences (such as the feelings of the people who don't like UBI).

Note that I think UBI is a great idea.

We're already giving free money to people, but at the moment we're giving money to people specifically for not working and for subjecting themselves to humiliating bureaucratic processes. So people get simultaneously rewarded and punished for not working.

Instead, let's just give them the money and give them some freedom.