I want to build a OW RPi4 router and want some suggestions for which USB3.0 gigabit ethernet dongle to buy. I don't want to build a module so what works out-of-the-box and what is reliable and fast? Amazon has so much for good prices.
Anything using the RTL8153 chipset should be fine. Personally I use the TP-Link UE300 and would recommend it.
As for working out of the box, it doesn't matter which USB dongle you buy, you will have to either add the relevant kernel modules and drivers to OpenWRT after install, build your own image, or use a custom build with the drivers already added (something like Rpi4 < $(community_build) would work).
No really needed, if you set up your RPI with a static IP, or dhcp client, on the existing ethernet port, you can utilize your current internet solution to DL the required packages.
The most common chipsets by far are Asix and Realtek. You definitely want Realtek for soiid out-of -the-box support and full 941mpbs throughput with low overhead.
The TP-Link UE300 is commonly used around here, everyone seems to like it. Another good choice is this from OWC/MacSales, they have metal cases and are robust and performant; I have two of them I keep around for when I need wired ethernet on laptops and the like.
If you need more than one additional NIC and don't want to occupy both USB3 ports, I can recommend this one. It's much more expensive than two of the singles, but it's worth it to me: it's what I'm using on my own RPI4 OpenWRT router. It's performant and stable on a very busy router on gigabit fiber with long uptimes.
(I'd also recommend increasing tweaking the cpu frequency governor to raise the minimum frequency to 1GHz from the default, and installing irqbalance.)
I have an older one, Trendnet model TU3-ETG H/W V1.0R. Uses the ax88179_178a kernel module. Not sure about v2.0. I am not using it with OpenWRT but linux is linux and that driver has been mainlined for a while now.
I use this :
I bought this D-Link DUB‑1312 no complaints as others have stated you need to either install via opkg the right kernel driver which implies an alternative router or build with it. I installed first time then when I upgraded to RC3 I built with it. For me it is rock solid.