I had an NH15. The design was pretty clunky, but DAMN it had so much power! It would back dirt up into the hose and still have 100% suction. It was such a pain to empty and the bin was really small, but the power made up for that. The head design was nice too, it curled up to get the edges of baseboards and under counters. The only Shark I know of to follow through on the claim - Never loses suction.
It is pretty ugly though.
It is pretty ugly though.