I'm in the lower middle class in Canada. About 15% of our income comes from government family support. We get about $700 a month for our two kids.
Our means test is "prove our two kids" and our tax return. Very simple to administer. No social workers to interiew us. The government does not care how we spend it.
This family support is a version of an incremental UBI. No Canadian political party will campaign against it. No governing party will abandon it. Too many people are on it. People like us will be upset with losing about $8000 a year in income, fodder for another political party to re-instate it. Familes with lower incomes will be more politically active.
No one is quitting their job to take on this support. That is an important reason for going gradual.
The social programs (in Canada) are changing often. The UBI will cause them to change in a different way. Many programs will be dismantled.