Dittos on the *itch bit in 5.2.x. In 5.4.1 it's pretty awesome. I've had a FSW-108D-POE at home off of a 60D-POE for nearly a year.
Read the document titled Manage FSW from FGT 54 ... and pay attention to the stacking section. With 5.4.1 only one switch is connected to the FortiGate on the port dedicated to FortiLink. The stacking section of that doc explains how to build a LAG on the FortiGate and enable stacking so that you can have the other end of your stack connected for failover in the event of a failure from that active.
FortiLink is not enabled on all ports of some switches by default ... the 48 port switches had FortiLink enabled from the factory only on the fiber ports.
LAG has to be built in CLI, no LAG between multiple switches (though I'm told that is coming).
No LAG on FortiLink ports (want more than a 1GB link, get switches with faster ports) ... hopefully this change will be coming.
I've got one in a 2-switch stack right now that's showing as offline, though it's still switching fine as a server and most of the desktops in this office are still talking fine. Support is looking into it so we're letting it float as is right now.
I've contemplated keeping the management ports connected as a back door from the FortiGate, though managing them away from the FortiGate could potentially create some issues... gotta discuss that with some engineers at some point.
Overall I'm liking the FortiSwitch and FortiAP management from the FortiGate. One last note... when upgrading FortiOS, be sure and read the release notes. On the home network I failed to upgrade the switch and AP before the Gate from 5.4 to 5.4.1... and it created some craziness that was resolved once the managed devices were upgraded. Lesson learned... upgrade switch and AP before Gate!
Fortinet XTreme Team USA (2015, 2016)
CISSP (2005), CISA (2007), NSE4 (2016)