Cheap Air Purifiers

Good portable cleaner but not as quiet as T300
I have Alen T300. It is whisper quiet unit with good performance. I wanted to buy smaller unit for bedroom and ordered T100 expecting it to be similar to T300. Only similarity between these two units though is design and HEPA filter - T300 uses two TF30 filters and T100 only one. T100 has also lower power consumption - 13Wt at low speed compared with 20Wt for T300. But it is louder - 39 db vs 36 db. Those 3 db make all the difference (3 db doubles audible sound level). When I sleep with T300 on in low speed I virtually do not hear it running when it is 5 feet away. But T100 sounds like air conditioner when running under same circumstances. And it additionally moves twice less air. Sound of motor and pitch of moving air in case of T100 is less pleasant than in T300. It all sums up to the fact that T100 is not for bedroom use. And even when I use it for other purposes its sound irritates if there is no other source of sound (like TV or PC).

I looked into interior of both units and discovered that motor-fan combo in T300 is higher quality than in T100. E.g. in T300 electric motor is open and seems traditional while in T300 it is closed design with closed bearings which reduces noise.

T100 pros are - it is small and portable, you can carry it with you anywhere you want. It does a good air cleaning - according to [...] it cleans air much better than typical value oriented purifier. Another plus is attractive design and ease of use. So I am thinking about buying another T300 to run in my bedroom while using T100 as portable air purifier.

Air Purifier
I purchased this for my daughter's dorm room to help with her allergies. It's a little noisy for the small area, but works well.

Small purifier
After having our kids test positively for air allergies, we wanted an air purifier for the kids bedroom. I was mostly concerned with the amount of particles filtered and the noise of the purifier fan. I was very price sensitive. I was treating this smaller unit as a test- if successful, we would buy a larger, more expensive unit for the entire house. All of the Alen products rated well in online reviews and consumer feedback. This unit uses the same filter as the larger 300 model and I would guess is a similar unit for a small room.
Because I cannot see the air particles, I am not 100% sure it works. But the kids seam happier and better rested. With the ionizer on, there is a pleasant 'spring-ish' smell to the air.
We are happy with this air purifier and will get a larger unit for the house. I will strongly consider another Alen model.

It was a present for my mom
I can't give a complete product review because this was a present for my mother who is asthmatic. It got there in great time and so far it's only been a month but she loves it and has said that it's not loud or extremely big. So for the price and the other good reviews I feel that this was a good buy!

Very quiet
It is expensive, but this is a very well made smooth unit that is very quiet. On medium it's still more quiet then the cheap fan in my computer. It does move a little bit of air, which can be cold if your sitting in front of it. So I moved it sideways, and now it does not blow air on me. The filter looks to be good with more cubic inches of actual filtration compared to the cheaper quacker box filtration units.