This definitely does what it's supposed to do. Auto senses when the heat turns on and boosts the airflow. I would give this 5 * except that it's a bit on the loud side because it's using two computer style fans to boost the air flow. They move a lot of air so I guess it's a compromise. My house is heat-only, so I am unable to review how well this works when using with AC.

Bought this to try to increase the amount of warm air coming into a bedroom on the north side of our house. It replaces a similar fan that sat on top of the floor register. The original fan failed after six years of constant use. The original fans were an experiment, but since they helped we decided to replace them with the flush mounted units. Our floor registers required the addition of the adapter plate, so measure carefully before ordering. The fans seem to work better than the older units they replaced. The room is definitely warmer. Have not been able to use these in the cooling mode yet, but based on my heating mode results, I think they will be just fine when we switch over next spring. The only negative for some may be the sound of the fans when running, but I found these to be no noisier than the units they replaced. Definitely not a problem vs. the increase in comfort.

Have a large master bedroom on the second floor and air flow was adequate but still too warm in the summer and cool in the winter. This seemed like a good alternative to reworking all the ducts which would include opening walls or a duct based booster. Arrived quickly and well packaged. Good instructions and appears to be pretty well made. Set it in the floor register, plugged it in, adjusted the turn on temp and that's it. Used the medium setting in heat mode, moved quite a bit of air. Helped the entire room reach a more consistent temp and was a couple of degrees warmer. The lights are a bit annoying as I like the room completely dark so colored them with permanent marker. As for noise, medium isn't too bad, more of a white noise type of sound. High on the other hand is too much, wondering id less restriction on the intake and exhaust sides would lower that?

Update: Purchased 31 Oct, mode switch quit functioning 11 Nov. Emailed vendor, no response. Returning.

This booster fan is noisy and feels like it moves no more air then the vent did without it. When it turns on, I can hear it 3 rooms away or even on the floor below. And simply removing the old flow restricting vent cover provided more heat to this room then when it had this so called booster fan installed.

Easy to install, does what it is intended to do. Like most homes the cool air out upstairs bedroom registers is low. this is a big improvement. Update--Worked well enough so I got another one. I may get two more (4 bedrooms total) they go on and off when they sense air flow and the DC fans do not use many watts to run. I measured like 3.7 Watts on high.