I first ran Pi-Hole on a Raspberry Pi Zero (non-WiFi model), with an RT-AC68U supplying its power and a UGreen USB Ethernet adapter. The performance at the time was perfectly acceptable. It was possible to run entirely over USB - one cable for power and data/network, but without Merlin, it needed some settings made in the router after any and every reboot, and thanks to some changes I'm not sure that setup would still work.
I then switched to an RPi4, before adding a second RPi4 for (unneeded) redundancy. And I've tried AdGuard Home too, but I'm now on Diversion on the router.
Each setup had its advantages and disadvantages, but as I can run diversion on the router, that's where I'm at. Frankly, if it's on an Asus router, and you don't want users to mess with it, then I really would go with Diversion, even if it's the only add-on you run on the router.
*I know I can (and I have) run AGH on the router, but it just doesn't seem so robust - to me at least!