I have been using light room 4 for a awhile now and find it works quite well, and has a simple interface for noise reduction. I happened to try a trial of Topaz DeNoise last week as I had heard good things, and had recently taken some photos at 20,000 ISO with my Mark iii that I wanted to clean up.
Long story short, maybe I didn't spend enough time learning the program but I found lightroom better & easier to use. If Topaz did do a better job it wasn't noticeable, at least not to me. If you are working off Elements, Topaz might be useful to you, but since I already have lightroom I saw no reason for me to spend the extra money for an additional noise reduction program.