ER tested an older version of FortiClient. I think CS tested a much newer FortiClient (but not 6.0.1) and it performed quite well, except with on-boot infections. CS declared FortiClient in the top tier along with products like ESET. However there was a major flaw in CS's test in that CS forgot to enable exploit protection which is a major protection component not functioning that launches before FortiClient proper so it might actually have passed the test.
Even so, without the adjunct technologies/hardware backing it up such as the FortiSandbox, you'd be wise to pair it with a solution like VoodooShield, OSArmor, Syshardener, etc. FortiClient and VoodooShield Free make a wonderful hardened combination for free that is actually very popular in some circles. FortiClient 6.5 is due out in a few weeks and should offer some interesting improvements.
FortiClient has 3 operational methods.
1) Vanilla, Freestanding - free version, no adjunct technologies.
2) FortiGate controlled - notched above free standing, allowing integration with FortiGuard+FortiSandbox, some endpoint control.
3) EMS - management portal for FortiClient that integrates ALL OF IT into an enterprise grade management, control and mitigation console.
As such, the free version should be considered minimum and pair with appropriate adjunct solutions and if you can handle some XML, make appropriate tweaks to harden it up and improve detection.