Two separate controllers is the complicated way to extend coverage — usually adding routing nodes is easier. But maybe we’re talking about a very large dead area where no coverage is necessary, so a second “island” of zwave makes sense. Problem then is that, over longer distances, ser2net can be unpredictable if latency or jitter increase, and you’ll keep dropping your fragile “serial” connection to the stick.
Your scenario might be a good case for using a Raspberry Pi Zero 2 with the Zooz ZAC93 controller hat — it just sits right on the top pins and the total cost is under $40. You install Ubuntu and Docker on it, and run ZUI container so that all the comms between it and HA are less latency-sensitive websockets (as opposed to highly latency-sensitive ser2net).
Or if your IP network is very reliable (i.e. wired) then ser2net should work ok, and the tubeszb controller (or WT32-ETH01 with ZAC93 running esphome you can DIY!) is a good fit. Unfortunately HAOS isn’t amenable to running a second add-on, so unless you use one of the workarounds above, a docker HA + 2xZUI install would be a more flexible approach. I’ve run two ZUI containers for years, with one usb connected and the other ser2net connected, with no issues (I only use the ser2net instance for testing though).