I have the Montbell Sprial Down #3 which is very similar to the Super Spiral. I love it. It is main bag. Being a big guy, I especially like the stretching ability. It also stays close to the body thereby eliminating air pockets. The nylon material is excellent in its water repelling.
One caveat, if you look closely at the specs, the #3 is rated a 40 degree bag with 30 degree as the limit. I have used it below 30 degrees and been comfortable. But I learned the hard way what clothing I need to wear.
I have used mine at least 100 nights with no loss of down, smell or wear. Well, my hiking partner, my yellow lab named Hunter, tore a hole in it using it as a play toy. He heard about my feelings and has never done that again! I still love him though.
Good luck in your choice,