The number one thing UBI doesn't handle well is rent inflation. You hand out $1000 dollars per person monthly, expect rents to go up by about $1000 monthly as landlords realise there is all this extra disposable income in peoples' hand right now.However, this is just an exaggerated effect of monopolies sucking out all aggregate disposable income out of economy that is already happening. Monopolies by definition don't have price down pressures, so they always price expand to capture anything people might have extra. Since landlording is the biggest aggregate monopoly in the world, landlords capture any disposable workers' income. No matter if they get a raise from their boss, the landlord always takes it away.

One of the biggest strengths of UBI is that it eliminates the beurocracy and waste associated with determining who "deserves" assistance. The dominant model in the US is expecting homeless people with drug problems to solve both their addiction and homelessness at the same time by themselves before they are deemed worthy of being helped, which needless to say is barely assistance at all. Having a gaurenteed income stream would make it easier to gain a foothold.