I've owned both and the only thing the Mini does better than an AR is not look evil. I also understand that is an important consideration for some, and if so the Mini is not a bad gun. Just way overpriced. When Mini's were selling for 1/3 the price of an AR I owned several. If I could buy one today for 1/3 the price of an AR I'd buy another. But with the prices being essentially the same, there is simply no way I'd put my money into one. If I already had one and was happy with it I'd probably keep it.
They are reliable enough, but not any more so than the AR's I've owned. The Mini's that have been shot extensively have not been able to hold up as well as the AR platform in long term heavy use. They were designed as an inexpensive farm/ranch rifle to be shot sparingly. They do this well enough with reasonable accuracy.
The AR's biggest advantages are much better accuracy, and much cheaper aftermarket and magazine support. Even the cheapest budget AR's I've used easily shot groups under 1" with good ammo. Never seen even a high dollar Mini Target gun that could match a cheap AR in accuracy. Good quality AR magazines can be found for $10-$12 anywhere vs $40-$50 for Ruger magazines, if you can find them.
I'd make that trade in a minute.