The version available from the purchase page on this site is 2.7.
This is identical to 2.6 except that it can now better handle the scenario where FSX Steam Edition (SE) and FSX are installed on the same computer at the same time. With 2.7 the libraries can be switched from one system to another and the correct FSX configuration file is used.
If you have a system with just FSX installed or just Steam Edition installed there is no advantage to 2.7 over 2.6 – they both work equally well.
You should receive an update email from the Flight Sim Store shortly