Best libre-alternative to FortiClient VPN?

Hi,

I have to set a VPN connection in a Trisquel 8 Mini machine.
The company uses FortiClient VPN, but the client for GNU+Linux seems proprietary and has no VPN capability...

Searching a little I've found this: https://blogs.gnome.org/lkundrak/2015/09/24/fortigate-ssl-vpn-support-added-to-networkmanager/

That GNOME post (from 2015) says that:

«With the availability of the new VPN plugin NetworkManager-fortisslvpn we address this [Fortigate SSL VPN]. On its backend it uses the free software protocol implementation openfortivpn (thanks to Adrien Vergé) that got some major improvements lately and integrates well with NetworkManager.»

NetworkManager seems to be the default network manager in Trisquel 8, so: should I install those packages? (I couldn't find them in Trisquel repositories so far.) Or is this already implemented by default and I'm good with just 'network-manager-openvpn-gnome'?
Should I try some other method?

If anyone have any experience with this VPN provider (FortiNet/FortiGuard/FortiClient) in Trisquel (or Ubuntu, I guess) it would be great to be able to avoid any proprietary package and stablish the connection anyway.

Thanks a lot for any advice!