Frosting

Has anyone made the frosting recipe with jar of Marshmellow Fluff in it???  I am looking for different frostings to try out and have been seeing this one lately....is it very sweet, hard to spread???  How have you used it???  also, I can remember the old classic 7 min. frosting....can these be used under fondant or should I just stick to my buttercream under fondant???....Some people do not like the sweetness of buttercream and I have used French buttercream (which is my favorite) especially when I used almond extract in it........I have also seen an Italian Buttercream which uses egg whites??? (that one was in the cake boss book)