I had asked the administrator of the expert flyer tool to compare his tool with that of the KVS tool. He sent me a private message with his responses, and gave me permission to post his response on FT. I will therefore quote his response.

Here is his response:

KVS and ExpertFlyer show different information because we get it from different sourcess. We buy it from the same airline reservation systems that travel agents use, KVS screen scrapes it from public websites. As such, we have access to information like enhanced Fare Rules and Routing Rules and upgrade and award information for certain airlines that KVS doesn't.

As far as features that EF has that KVS doesn't:
- Flight Alerts (the ability to be emailed when inventory on a flight opens up, either award, upgrade, or normal fare inventory).
- The ability to save searches so you don't have to type them again later.
- All our information is available on our mobile version at mobile.expertflyer.com
- Graphical seat maps for over 100 airlines (list of airlines here: http://www.expertflyer.com/sessionlessSeatMapList.do)
- Ability to see exactly how many award/upgrade seats are available for the airlines we support, not just a Yes/No answer

Also, all the information on your subscription and free trial is easily viewable on the Subscription tab on the My Account page, which is linked to from the top of the left side menu after you login.

Also you can find full documentation of all of our functions here: http://www.expertflyer.com/support.jsp

-EFV