If this expense is compensated by extra taxes on individuals then it is pointless.
If it means making sure that unemployed people receive a guaranteed minimum income then it already exists.
If it means merging all benefits into a single one then it is just a simplication and also already exists, e.g. recently in the UK.
UBI, as in 'everyone gets a payment', only makes sense if there is a source of wealth that does not depend on people to tap into. That's why it is often discussed in the context of massive automation, because then it has merit (basically robots work and you receive their 'wages').
In my example, which is what this trial does, it is plainly unaffordable.
That's a good summary of UBI, actually: It's great, please let's not get bogged down on details like financing.
Yes, with UBI we're basically taxing ourselves to pay ourselves, it will hurt productivity and will cause inflation.
But at least in a country like Germany, where I live, that is already happening for decades via our ever-growing, convoluted, amounts of government welfare programs, subsidies and redistribution schemes.
A UBI would then at least have the benefit of cutting out the bureaucrat middle man.