I ordered the Flint 2 a few days ago. I can report back how it is once it arrives. Sucks that I have to buy a second router, but the Asus one I originally got has been a real pain.
I've been using a Flint 2 for the better part of a year. No complaints. I was used to a decent Asus router and replaced it when it went end-of-life because the OpenWRT firmware for the ASUS device wasn't feature-complete.
I installed vanilla OpenWRT as soon as I took the Flint 2 of the box and I ran into no major issues. I only need to focus on home use with wired and wireless clients, plus a network printer. The web interface works as advertised, as has the command line interface to the extent that I've played around with it. Once I dealt with the basic setup, I've been able to forget that it's there other than to install new updates when they become available. Whenever I feel like it, I'll see about installing some services like router-level vpn or network adblocking. Not a priority yet, plus I like doing clean installs when I update the router firmware.
I haven't used it but have been reading around various devices for the best part of a year and I really like the Banana Pi BPi-R4. It's not perfect, but it's a decent device. I would use it with a seperate AP though.
I just did this. I installed a banana pi r4 as my main router with no wifi, and a couple of separate APs. I bought some Extreme Networks APs on ebay for USD$15 each, already flashed with openwrt.
I used the YouTube tutorials by OneMarcFifty to set up vlans for alternate SSIDs. Works great!