Cisco is an Enterprise/ISP/Government provider so no third party stuff will run. They have NIST and FIPS standards they must follow in order to be able to sell into those spaces.
You may be able to get some of their old Linksys by Cisco stuff to run tomato but I think they sold that product line off to Belkin who killed it.
Unfortunately most of the features of their devices are only available through their licensing. Also you won’t be able to get updates to it without a support contract. Even if new it generally isn’t worth using at home.
Not sure if using a network device with no security updates and a firmware that might be found online is worth it. Also, I would never flash a networking device with a firmware that is found on a random website. After all that, most of the features of Cisco devices are still locked behind a license key.
It being a 100 Mbps ("Fast" Ethernet) switched router, it's really only useful for devices that don't need or use more than 100 Mbps network speed, so like PoE IoT devices perhaps.
That's true, but because of that you can get Cisco certifications, which could be helpful if you end up in an network related job. Those certifications will also give you a lot of knowledge of how networks work. (I'm currently completing a CCNA, and quite enjoy it)
A few other companies also clone the Cisco CLI, so there's that too. I wouldn't touch the Web UI if it has one though.
Security cameras with a central continuous recording system + alerts and automations… plenty of fun to be had. Also wifi access points on poe depending on the interface speed. Got those 2 at home and it has been a treat so far.