HAOS installed sucessfully. But it does seems slow, even with basically nothing running on it but HACS, the SSH addon, and the file editor. And yeah, I think it’s a 3B+ here too. From what I’ve seen in terms of recommendations, you should use at least use a RPi 4 or a NUC though.

As to containerization: Afaiu, all versions of Home Assistant are containerized which automatically makes them heavier than they’d need to be. The difference between HAOS and container Home Assistant is that HAOS is a full Linux distro with multiple Docker containers preinstalled on it, whereas with the containerized Home Assistant you set up your own OS and then run those same Docker containers on it (or perhaps it’s just one Docker container, haven’t tried that).

As to the integrations, both devices have Modbus and there are (plugins? integrations?) for them, so I am hopeful there, although I haven’t figured it all out yet.