This Transceiver is not certified by Fortinet

@esa12 

This is a warning message for this , you can find details in below KB 

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Transceiver-not-certified-by-Fortinet/ta-p/325528

Nope, it (transceiver)   either works or not from the start. This warning is more of a disclaimer type - "If you have some problem that Fortinet TAC will attribute to the transceiver, they will not debug it". 

We have used/use both - certified and not, and haven't had any case of it being a problem. More depends on quality of the transceiver itself - if you buy cheapo SPF for 50$ it will cause problems whether you use it in Fortigate or Cisco and the problem will be obvious anyway.  

We never used SFPs cost more than US$50 at least for last 15 years with our customer serving FGTs. None of them are certified by FTNT. But we always choose "FTNT/FGT compatible" if there is an option, and avoid some brands that went bad in a couple of years in the past.

Toshi