They seem to help with my families' allergies. We use the Coway Mighty Smarter Air Purifier with Eco Mode. You can get it on Amazon or Bed Bath and Beyond.
Bought one about a year ago and think it has really helped with allergies. Spent a lot of time researching and settled on the RabbitAir. Definitely on the expensive side, but was consistently well reviewed, so decided it was worth it.