I am European, I have been in most of the EU big capitals and many other cities, never seen free public transport and I almost never even heard of it.

Free transit is mostly an edge case. It's almost always limited to small cities or municipal areas (including in Europe), and often target the elderly and students. There are interesting consequences to free public transit, such as picking up some new kinds of riders at the same time as turning off other riders. But it can be pretty effective in the right cases.

Baltimore has a free shuttle bus called the Charm City Circulator. It's not intended to move people around the city. Instead it's targeted at a central problem area that may otherwise be prone to increased traffic congestion, pollution, and slower or lower ridership. It also facilitates tourism and gives an incentive for workers to live in/near the downtown area.

The CCC is popular enough that it's hard to get on one heading downtown in the mornings because they're so packed with people heading to work. And strangely enough, it's much cleaner and with fewer undesirable riders than regular (paid) buses in the city. This is probably due to the historically segregated layout of the city and the particular routes these buses take. The biggest problem with the CCC is it hasn't been funded or maintained properly, so these strange custom shuttles are breaking down and there's nothing to replace them. As a result they had to cut down some of the routes, while they also expanded the most popular route to travel farther north.

It’s not free though. So figure out how much of your tax goes towards public transportation and _then_ compare.