We go to 5 Guys a couple of times a month as a family. As stated, they don't have a WOW factor, but the food is fresh, completed as ordered, and served with a smile. Not many places give you vinegar for your fries, and we appreciate that they do. The kids never complain about going there, and I do like the peanuts. Overall, it is a good experience, and I do not consider them fast food. They just don't seem like a Burger King or Wendy's. They seem more like a neighborhood lunch shop, or something.
BTW, on the peanut allergy issue, the local stores around here have a sign on the door warning people about the presence of peanuts.