We were in the market for an air purifying system because our house seemed to always be dusty regardless of regular vacuuming and dusting. After several hours of researching and reading online reviews, I settled on the Alen BreatheSmart 45i True HEPA Air Purifier. We needed something that could purify the air in a 650-700 sqft open floor plan. This model is rated for 800sqft on the Turbo (highest) setting). I also wanted a unit that would tell me how clean (or in our case, dirty) the air being filtered is. This unit also has an option to dim all of the lights on the unit which is perfect for sleeping. The unit is slightly noisy when on the highest setting, but once you get used to the noise you almost forget that it's on. I've now had the unit 2 weeks and we leave it running 24/7. In this amount of time I've vacuumed the pre-filter twice, so it is definitely working well. I can't speak for the longevity of these units, but so far we are very pleased.