I've been running 5.4 beta and beyond since XTreme Team last fall and haven't had a single problem... granted the beta was only running on a 60D-POE in our SecOps Center, so it wasn't being pushed very hard. We did find some cosmetic issues that were fixed in the GA, but no bugs.
I've now got it on a couple of 60Ds and a 90D. We're about to have to put it on a couple of 100Ds in order to support 48 port FortiSwitches. I will hopefully have four 3700Ds going online late August or September that will need it to support the high end FortiSwitches. I'm certain Fortinet will make sure those puppies are stable.
CyberNorris - how is 5.41 running on the 100Ds? Ive got a big 6-location site in south amer backhauling through one big office, currently running about 200U on a 100D on 30M fiber (i know, i know). Lots & lots of shaping and UTM, not doing full SSL inspect yet just certificate, but very soon (with AD auth). A bunch of IPSEC tunnels & an SSL VPN for outside users.
It's on 5.10 now, and i finally got a spare down there that i'm tempted to either put 5.26 on (less bugs than some of the latter 5.2x since we use SSL VPNs!) or take the plunge on 5.4.1. Definitely an important site that can't be down, but i have the luxury of the existing 5.10 box i can have onsite team swap back in in a jiffy.
I've personally had no problems with 5.4, even back to the beta, though I only ran the beta at home. I only took a couple of 60D/90D to 5.4.0, but have moved a few more to 5.4.1.
Everything else is 5.2.6 to 5.2.8 due to published vulnerabilities.
The 100D that we took up has had no problems, though there was a small issue with FortiLink stacking flapping, but the latest switch firmware appears to have fixed that. Let me say that the switching never failed, it was just FortiLink that was flapping.
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