Maximizing throughput on old routers, plus luci's "realtime graphs" -> "connections" tab

Well, cisco and friends tell you which modules their routers/switches are compatible with, if you select others you are on your own... this is decidedly not the plug and play world we learned from the PC...

Nobody said that $$$ use USB extensively, my claim is that for a home user the chance of getting a random USB dongle to operate on an OpenWrt/Linux router is larger than getting a random SFP module working, assuming the router actually has a SFP cage to begin with. (My turris omnis does and I monitor the SFP threads over in their forum, and it still is a bit hit and miss, actually the situation is so bad that team turris created their own (rebranded?) 1/2.5/5/10 Gbps Ethernet SFP module (for twisted pair copper wiring) that allows 2.5 Gbps operation on the omnia, I am sure if the commercial SFP situation wasn't as problematic as it is they probably would not have bothered.

Sidenote: the one thing where SFP and similar shine is if a router/switch/server is supposed to be used with mixed physical ports (copper, different fiber variants,...) then being able to switch out/between different physical layer modules is attractive (and a reason why big iron vendors offer that), but again big iron vendors will likely not guarantee that all possible SFP/whatever modules will work on their gear.

The thing is that the “only original SFP module works” thing disappears if you install non original firmware.

But it is not that many manufacturers that actually locks their SFP. Cisco is one but they are like Dell, only their stuff or nothing at all.