I've been looking to do something similar, but I've been leaning toward the opnsense route with a little htpc with two 2.5G ethernet ports, but haven't pulled the trigger yet.

Mostly because my 10yr old unifi USG still works.

IIRC, Merlin is built from the Asus firmware, so Merlin is very stable and somewhat more featureful and secure than Asus vanilla. I have been happy with it for years, having moved off of openwrt and ddwrt.

Merlin does not aim to accomplish the same as something like openwrt, which is a larger project and lends itself to more involved customization and etc.

When it was just me, I could tinker but we were working from home and now we have kids with internet use also.

Basically, I use Merlin because I want more features but i cannot really tinker with it; the WiFi is our production environment. I considered having an internal lab network but it just wasnt worth the overhead.

I've loved my Flint 2. Being powerful enough to run my VPN and a pretty stout adguard home setup has been huge.