Just to add another echo to what has already been said, the AD2 is more than adequate for home/personal use. If you are at or above the weight limit, I wouldn't be doing "sprints" on it. That being said, I was 300lbs and used one regularly.
Schwinn sets the standard for resistance/fan bikes and in my opinion the Airdyne can't be beat. I must be honest, however, and admit that I own an "Airgometer" that I bought off of Craigslist for $50. When outfitting my home gym, an actual Airdyne was not my highest priority.
In the beginning, I got a bunch of stuff on the cheap (Half-Rack with bar and weights for $200) and only trained at home in a pinch since I had regular access to a nice facility. As I have enjoyed training at home more and more, I added a nice bar and just recently purchased a nice rack/bench from EliteFTS. An AD6 is on the list, but still not a HIGH priority. The "Airgometer" is serving its purpose just fine.