Establish IPSec VPN with F5 Big-IP and Fortigate 30C

You're correct that IPSec VPN (IP ESP) of BigIP is still unstable in most cross-vendor implementations. As of now, only consider using BigIP as a peer in IPSec VPN implementation when it's paired with ASA, or another BigIP. In various other setups, I have always concluded the stability is just not good. In regards to SSL VPN which is an entirely different thing, I find BigIP to be very stable.