This is the correct answer, always single mode. It's been the most future proof to date, people just keep figuring out how to cram more and more wavelengths into it.
Good to know! Not sure why I am so often shy on getting used. I've done it when the deals are simply very good, but that's just been with referb harddrives (with a warranty) and this switch, which was just too good of a deal. I gotta get braver there.
The modules/transceivers are unlocked there, but the switch ports may not be. Mikrotik doesn't vendor lock their ports, but the bigger manufacturers do. Some places sell transceiver programmers, but those are locked to their own modules (I think that may be due to a technical limitation). So fs.com's modules can be reprogrammed with FS.com's fiber box thing, and ubiquiti's modules can be reprogrammed with their Ubiquiti Fiber Wizard (I think that's the name of it?).
My switch has vendor locked ports, and there's a console command to disable the lock, but I'd have to beg the manufacturer for an unlock key (it's based on the switch's serial I believe) for a key, and it's a used switch, and they are not a fan of people using their OS on used switches since their license entitlements are non-transferable. So it's FS for me, and if my next used switch is a different brand I'll have to shell out for their reprogrammer.
Wiitek is a brand with the lower wattage ones that run around 60°C, not sure if they are on AliExpress, but they are on amazon.ca and worked perfectly in my Mikrotik. To OP and other readers, if getting into switches with transceivers be aware that many enterprise networking gear vendors vendor lock their ports and transceivers. That was an expensive lesson for me. There are third parties selling off-brand transceivers for a lot cheaper than the branded ones (fs.com is probably the biggest and best known). This can get complicated if you have different manufacturers and need different coded transceivers or even DACs with different "brands" on each end.
Nice score on the used switch! I used a 10GbE Mikrotik up until recently until it started having hardware failures (my second one, a few years older is running perfectly, been very happy with it). I got exceptionally lucky finding a used 64 port 40/100Gbps enterprise switch on ebay for $1000CAD (same switch here normally goes for $3-4k CAD used). Most of my ceph cluster is limited to 10Gbps (onboard RJ45 for 4/5 nodes, and the PCI-E slot on each is taken by NVMe drives), but I feel I'm already outgrowing that speed, my few nodes already saturate 10Gbps - NVMe drives are fast! Now I just gotta wait for 100GbE NICs to come down in price, I'm not sure I'm ready to buy a used NIC yet (was nervous about the switch, first used piece of network gear for me), but the knock off Intels are like $350 minimum here for a 2 port.
The repair ability is why I went with a Framework. My last two laptops had keyboards that lasted until a few months after the warranty. Rest of the laptop works, but I can't find replacement keyboards at a reasonable price. So a framework, and I bought a spare keyboard upfront on the off chance they go bankrupt.
While I love the Internet and all sorts of modern life fixtures (in a developed country), I feel a bit like I missed out by not being alive when all the crazy drinks were around.
Our child is only 6 but these fears are done of the reasons we have immich at home (amongst other things). We still have Google storage for photos, but just in case they take a photo or video that gets flagged we do not want to lose everything. I am though trying to get in the habit of having an annual photo book printed to have some used copies of memories.
My spouse is more tired to Google, but for myself if I got cut off i'd just have to change some recovery email addresses.