Your statements in the 3rd paragraph are incorrect.
There is no ongoing trial, just a plan to have a trial start in about a year. The parameters (e.g. location, the monetary sums, exactly which existing social security mechanisms it replaces) are still undecided. But it seems very unlikely that they'd run the test in just a single location like you're suggesting.
It is also not being pushed by a left-wing minority, but by the most conservative government Finland has had in decades (consisting of the conservative party, the centre party and the nationalist party). At least right now the idea appears to have very broad support in the polls, though that could of course change once there's a concrete proposal.