Fiber isn't ubiquitous, you can't just buy any media converter.
I recommend you stick to: TP-LINK MC220L
That is what I use and I can confirm it works with their supplied miniGBIC.
You basically buy the converter and remove the miniGBIC from the router and plug it into the TP-Link MC220L.
Then plug a network cable into the TP-Link MC220L that goes to your router.
Your router must support VLANs on WAN.
Many routers do support this however.
If you aren't technically inclined just buy a Wifi router and plug it into the router they supplied.
I got my details to my account on a printed piece of paper.
But you may be able to get it from the router.
The general settings is that they are on a VLAN (ID = 100, but that could be local to Cape Town).
You make a PPPoE connection with a username and password on that VLAN.
My main point here was that lightspeed was a company offering retail customers the latest in technology with fibre internet, yet they default to a wired modem when most of their retail customers (if not all) would have a need for wifi with phones/ipads/etc.
It is still early days, their technology choices are likely very limited at the moment.
My guess as to why they limit the Wifi on the router is probably due to ICASA restrictions.
Cybersmart have their own Speedtest servers that sit pretty close to the main transit centers.
So as I said, it is more a test of your physical connection and that it is, in actual fact, capable of whatever speed you set your line to.
What you get internationally depends on where you are connecting.