I am a business traveler and fly many miles a year. I purchased an upgraded seat to extended seating, and unfortunately selected an aisle seat since there were no window seats (my preference) available. When I checked in on line, I notice that my boarding group is 4, or virtually last. I have immediate concern, as I know the aisle seat area where personal belongings go is smaller than the other seats, and also know that there would be no overhead bin space by the time I boarded. I had a larger than normal briefcase with me, and asked 2 individuals with United if it would fit under the aisle seat. I was assured it would (I also measured it with their "box" at airport). Well, as expected, by the time I board there is no room above, the seat area is so small that I literally have to jamb it under the seat (and it even stuck out a little bit into the aisle) and there is no room for my feet or my purse. Fortunately the woman sitting next to me was kind and allowed me to place my purse under her seat. I was so frustrated! I a mileage plus member (which obviously means nothing) and the people don't know their planes very well. When you purchase an upgrade, you should be allowed to board in group 2 or even 3-who cares if you have to get up and let someone in the middle, when most of us just need carry on space and extra legroom? Purchasing the upgrade was a complete waste. And the plane was freezing. Miserable flight. It reminded me why this airline is not my first choice and I only fly them when I don't have other options that work with my schedule.