Mini Coopers are tiny cars, but they are as reliable as a BMW and they have excellent handling.
They are overpriced, in my opinion.
There are Subarus, Nissans and Hondas that cost less, get about the same mileage and have more space. To some they are less cute.
I suspect people buy them because they are distinctive and European. Japanese cars are reliable, but they are far less likely to become "collectables".
I would take a Subaru WRX over a Mini Cooper, personally. Maintenance, according to Consumers Reports would cost less.