Nokian winter tires are nothing short of amazing, stud them and it's unstoppable. I run the studless on my other vehicles, have a set in the factory 20" size on order for my MX. Last winter in Montana I drove with the then new all seasons (received my car mid January). The car handled reasonably well, but certainly not as good as my previous car with the Nokians. This winter I decided to buy true winter tires rather than "get by" with half worn out all seasons. (14k miles).
In my opinion, those who say it does "fine" with all seasons have never experienced driving with a true, high end snow tire such as Nokian. There really is a difference. If you live in an actual winter climate such as Montana where you will be driving on snow covered roads a considerable amount of time, it's well worth the investment. If you occasionally see snow, I'd stick with the all seasons, the AWD system works quite well and the car is heavier than a normal car due to the battery.
You will take a slight range hit and snow tires do wear faster on pavement.