Redistributing income can be expected to cause market-specific price increases in goods that the people benefiting from the redistribution have a greater propensity to purchase than those from whom income is redistributed. (And decreases in other goods.)

Adopting Basic Income is pretty clearly going to affect a redistribution of income.

So, the increase in prices for basic goods conclusion is sound (the idea that this will end up harming those just above the poverty line by giving them less purchasing power seems, however, far less sound.)

Its not like marginal propensity to consume of people in different income levels is a completely opaque mystery about which we have no information.

Not to determine short-term demand effects of redistribution of income there isn't.

> And I'm not sure if this degree of raise in income practically changes marginal propensity to consume that much.

Probably not, but since marginal propensity to consume is the amount of the next dollar of income that will go to consumption, that means that the consumption effects are fairly straightforward if you have an idea of marginal propensity to consume.