We bought the 211+ model about 2 years ago.  It has functioned very well, especially during the nearby wildfires here in the Sierra Foothills.  It made a huge difference in terms of the indoor air quality over what we experienced without it in the past.  It also helps clear the air when we get a bit of smoke in the kitchen.  Although it's a moderately sized unit, it fits in well.  We've ordered a second one to keep in our bedroom.