I am not doing Anyconnects nowadays, but work with Forticlients a lot and mostly the experience is good. They do have, as all vendors I guess, catch up to do with the newer operating systems/standards/OSes, but usually it happens with some delay. Like, Apple & macOS are being released obviously faster than Fortinet can QA FC on them. Browsers hardening their TLS settings also faster than FC does it, like limit on FGT SSL VPN protocols to TLS 1.3 only and FC will stop connecting on Windows 10, while Web Mode SSL VPN via browser on the same PC will work with TLS 1.3 only just fine.
Regards to FC free VPN-only vs EMS full versions, I haven't noticed differences. My guess is that Fortinet use the same code base for VPN in both clients.
Edit: Also take into account the Survivorship Bias - people who use FC and have no problems with it will not post here on forums or elsewhere, I am yet to see a post "HI, just came to post that my Fortigates and Forticlients work just fine and I am happy" :)