I have been running (in Node-RED) flows to read my solar inverter and battery information into Home Assistant for several years. I use Ethernet TCP adapters to interface to the various serial ports, and have recently changed the physical devices used.
Pusr produce a wide range of units, and recently introduced the ‘lipstick’ range. I now have three of these, replacing all my existing, much larger, adapters.
They are indeed small, DIN rail mount, power from 5-24 volts (I am using a 24v volt supply). Each one has only one port, so I have three - one for RS232, one for RS485 that is acting as a Modbus Gateway, and one for CANbus.
Performance appears rock solid, not that I have ever had a problem with the previous units. Setup is via webpage and easy to do, except for the CANbus which is configured via setup software (download from site).
The prices are also good, having obtained the serial units for around £12, although the CANbus was more expensive (presumably because there is much less demand for CANbus).
CANbus [USR-CAN115] can be set as mono directional (listen only), and has package filtering capabilities. I just run this as a listen-only TCP server and receive a copy of the CAN messages broadcast between battery and inverter, getting back the full block of information and the inverter reply heartbeat every second.
RS232 [USR-DR-132] is straightforward. This unit also has Modbus capability, but I just use it for serial message & reply to read from the battery console port.
RS485 [USR-DR-134] unit has many features to support Modbus, so reads and writes via Modbus TCP are easy. Again I just use this for Modbus-TCP to Modbus-RTU conversion, but there is an MQTT gateway and much more. The unit (apparently - I have not tested this) can do multi-host polling and edge computing, where the unit itself polls Modbus registers, maintaining an internal JSON record that can be read when required.
Connections to power and comms at the bottom connector are good, although with a unit this small the ethernet connection is at the top end and might well benefit from a right-angle plug (to the side), although I suspect that the specialist cable would end up costing more than the adapter.
For myself I prefer the reliability of cable, but WiFi models are apparently also available.
Looking around I can currently see these units as low as around £12-15 (UK) each.
The three units take up less room that one unit did, so my only problem now is to tidy the wiring, and to work out what to do with the unused space.