From FortiOS 4.x to 5.0.x Fortinet was soundly in the 'average' territory at best. They started pouring resources into R&D and expansion of their threat lab and analyst personnel in FortiOS 5.2.x. This took several years to mature, culminating in the overdue 5.4.x series. But 5.6.x pushes Fortinet into new, more powerful territories for sure and it should be considered one of the premier UTM/NGFW enterprise grade devices. It's exceeded expectations with all of the certification labs without a doubt and is a leader in ROI among the top players.
FortiClient has benefited some from these advances but more R&D is going into it by the month because of the EMS as part of the Security Fabric. The end goal is to make FortiClient a word class endpoint threat management solution. Which is why from 5.6.0 to 5.6.2 you've seen many features and technology added, such as the anti-exploit module. This advancement will continue as the EMS is pushed for wide adoption.
Watch: An Introduction to FortiClient EMS
Free users benefit from a portion of all of these advances but must realize they won't benefit from all of them simply because of the fact they don't have the EMS or a FortiGate deployed, nor the incredibly important FortiSandbox.
They'll still have world class signatures (including Zoo if enabled), Solid Heuristics, Fantastic Web Filtration, Exploit Protection and Dynamic Threat Detection. All of which should be sufficient for general home use as a free solution, especially considering the power of its web filtration. The real way to test FortiClient is to toss it on a test machine on a DMZ and let people hammer it until it dies. Let me know the results then. (glances over at the lab with dozens of honeypot boxes doing just that) You might be surprised. Hence, my recommendation of FortiClient for folks looking for a free solution not full of cleaners, optimizers, widgets, gadgets and gizmos - just solid protection.
Something to keep in mind on the latest AVC Real World Results where FortiClient scored 98.9% - 1) They were using 5.6 proper, not 5.6.2 - which has additional protection/features.. 2) They didn't have FortiSandbox active on the FortiGate. So while they did test it behind a FortiGate, a crucial component was missing when tested, that FortiSandbox is the ATP/Zero Day detection unit.