Awesome, cost effective, efficient solution :).
People can get way too hung up on worrying about the methodologies surrounding sound absorption. The fact of the matter, is that you don't need an artificially dead room in order to get a reasonably balanced mix to your ears. Proper speaker placement, along with decoupling your speakers from the desk (sit them on some big foam blocks), and keeping a careful ear on/being aware of any standing waves or resonance peaks that your room exhibits. If you are having problems with excess bass, try plugging the ports on your monitors. This'll reduce the artificially enhanced sub-bass, but it will help to really tighten up your higher-subs and low-mids.
If you have the space, some spare time, and a little bit of cash, build a bass trap or two, like rigs. But diffusers? You don't need them, you don't have hundreds of thousands of $$$ worth of mastering gear, and you probably won't be able to figure out the maths to make your system work effectively.