I used them for our upcoming trip. I booked a flight via United. So far so good. The price they quoted had all the taxes and fees included, so no surprises there. The taxes and fees for four tickets were $200! Also, United changed the flight once (by a few minutes), and Expedia notified us right away. They also suggested that I call United to confirm flight. I did, and United had the reservation in their system and were very nice.
I hope this helps.