ProFlightSimulator is
FlightGear, a free flight sim that has been packaged up to save people the trouble of having to spend hours downloading everything that is included in the DVD set.
If you look halfway down the page that you have linked to, you'll find this :
ProFlightSimulator is proudly part of the Open Source community and is based on the world renown FlightGear project. This means this flight simulator download is in constant development and keeps getting better and better.
It's not all that bad, just remember, that you can get everything in ProFlightSimulator for free, and what you are actually paying for here, is the DVDs & the time you don't have to spend downloading everything.
If you'd like to "try before you buy" Simviation carries this Sim for Free download, as well as several nice addons for it.
http://simviation.com/1/browse-FlightGear-110-1I have FlightGear running on my system,
here is a shot over San Fransisco to give you an idea of what you're getting:
[img]http://www.simviation.com/yabbuploads/SGFG4b[1].jpg[/img]