Albeit a bit expensive, Turris Omnia is fully open source down to schematics level. It's also pretty beefy with dual-core ARM CPU at 1.6 GHz and 1 GB DDR3.
Its documentation is however a bit lacking unfortunately.
Been running a home network with over ten devices and a fast internet connection with an Omnia Turris for almost two years now. It gets regular updates automatically, is fast and the UI is nice. Fixing things like bufferbloat was easy with the community instructions.
Oh and it's openwrt under the hood, with lxc containers for things such as grafana.
Careful if you started using lxc like I did before they added warnings not to use them with the internal flash storage. You need to have added additional storage via the mSATA slot, and designate that as your storage location before using lxc. Otherwise according to Turris you will burn through your internal memory very quickly.
Oh and it's openwrt under the hood, with lxc containers for things such as grafana.