This can also be set up graphically using OpenWRT (which is a lighter-weight OS if you just want to do some networking and not use the Pi for anything else.
I should note that while the onboard WiFi is 802.11ac, I've never seen it get more than 60-70 Mbps in my own testing (in a variety of network environments), so if you want more speed, you might want to get an old n or ac router and flash it with OpenWRT instead.
What operating frequency did you use? I got the RPi4 mentioned in the article and I run OpenWrt on it as my home router. I got it configured to AC mode, 40 MHz width, and I easily hit 100Mbps.
I live in an apartment though, I wouldn't trust it to cover much of a house. Also it's struggling with keeping 10+ devices connected. But speed is not bad! I prefer it over the retail routers I got hooked up as access points.
Yes, those speeds are roughly consistent with what I got in my speed tests here :)
You (and others in these comments) have suggested using OpenWRT as an alternative. I suppose one advantage of the approach outlined in the submitted article is that you can still use the pi for other tasks using the normal raspberry pi OS, instead of installing the OpenWRT OS.
I should note that while the onboard WiFi is 802.11ac, I've never seen it get more than 60-70 Mbps in my own testing (in a variety of network environments), so if you want more speed, you might want to get an old n or ac router and flash it with OpenWRT instead.