It's a bit tricky to review a product that makes health claims (for instance, this product offers an "allergy relief guarantee"), so I'll instead focus on the benefits and drawbacks that you'll find in daily use.
First, some basics about the Fit50 Air Purifier. This is an attractive product, clearly designed with an upscale look appropriate for the price. This is not a throw-away gadget that you might find in a convenience store. It's a serious appliance. Second, this appears to be a newer, lower-capacity version of Alen's $600 product, which is rated for 1100sf, whereas this one is rated for 800sf. The other differences appear to be an updated, more streamlined control panel, and a smaller overall size.
On to actual usage. After about two weeks of use, this is what I can say about the product:
(1) Air Quality: The Fit50 has had a dramatic impact on the air quality in the master bedroom/bathroom suite I've used it in. We typically leave the door closed to keep warm air in, but that previously led to a stale air smell. With this air purifier running, the air in the room is now the freshest in the house, despite the door always being closed.
(2) Auto Mode: The auto-detection setting is a nice feature (responding to particulates in the air by increasing speed), but I think it's a bit over-sensitive. The purifier ramps up every time I make the bed, probably due to large dust particles being kicked up, and also responds to the use of the shower, probably due to water vapor. Overall, it just seems to ramp up and down too much. While it's supposed to have three detection settings (blue for clean, yellow for moderate particulates, red for heavy particulates), it constantly jumps from blue to red and back again. I've never seen the yellow indicator. Frankly, when I have the filter running 24 hours a day and nothing is happening in a room, I don't believe it should jump from clean to dirty to clean within a few minutes, over and over again. Something seems off about the detection system. I really like the idea of knowing what the quality of air is in the room, I'm just not certain I can completely trust the Fit50's assessment.
(3) Timing Controls: There is a timer feature, which allows you to set it to shut off after 2, 4, or 6 hours, which is great if you just want it to clean up the air when you leave, and then shut off, or perhaps run right before you go to bed but not all night. Even better would be a programmable feature, which would require the addition of a clock, which this unit does not have. I'd love to be able to tell it to turn on at 5pm-9pm every day to clean up the air before arriving/going to bed.
(4) Noise/Lights: On the lowest setting, the unit is not particularly noisy, just a smooth fan noise, but on the three faster settings, it's quite noticeable. You won't want it on anything but the lowest setting when sleeping. One thoughtful feature is the ability to shut off all display lights, for instance at night. The lights are very helpful when adjusting settings, but they are also very bright, so it's great to have the ability to turn them off (by pressing the power button a second time).
(5) Cooling Effect: A side effect of having the unit running is that a lot of cool near-ground air is forced upwards through the unit's top-mounted grill, which then falls back down in a large radius around the unit. Even ten feet from it, a constant cool breeze can be felt. This may be nice in the summer, but during winter months, a cool breeze may not be what you want, especially in a bedroom. In a small room, it will be hard to avoid the cool breeze effect, which is a drawback to the use of this unit in cold temperatures.
(6) Energy Use: Using a watt meter, I found that the Fit50 draws 39W at speed level 1, 46W at speed 2, 55W at speed 3, and 64W in Turbo Mode. Depending on your electricity rates, it will cost about 10-15 cents per day to operate 24/7. That's about the same as a small room fan, and this product does so much more, suggesting that it was designed with high-quality, energy-efficient components.
Overall, I am very pleased with the Fit50 HEPA Air Purifier. I had previously used a small, inexpensive air purifier, and it did almost nothing to improve the quality of the air in the room. This product most definitely does improve the freshness of the air. As for the product's health claims, I can't back them up, but I do sleep a bit better when the air is fresher. The cost of the product is daunting given the difficulty in assessing the health claims, but I know for sure that ti's far better than the ~$100 product I used previously.
Pros: Easy to Use, High Quality, Nice Design