We had one of each back to back for extended test drives. The mini was fun, well built, certainly not small and we didn't get anywhere close to 38mpg, even with my wife driving we achieved quite a bit less than that. We borrowed an ex BMW management car, so it had all the bells and whistles, pretty much every extra all for a huge saving on list. The Abarth just made us smile, fits like a training shoe, goes like stink, we loved it. The only slight gripe we had was around the seats, they needed a little more padding for our liking, but certainly not like sitting on a orange box. We didn't get either in the end, however the Abarth will be added to the stable at some point.
I'd say when the world resumes some normality get in both and try them out. They are different, both great cars and enjoyable and I'm glad we did the back to back extended test drives just because neither car was exactly what we thought ( in a good way)