UBI is only relevant if it's universal. Doing such a study on a small sample is rather irrelevant and inconclusive.

A better idea might be to do it in a village and compare with another village that doesn't have it. But even this cannot fully replicate the nation wide effects of UBI. How about immigration laws? Germany is in EU, anyone can move to Germany and ask for UBI.

Waste of effort and money to prove nothing.