I'm posting this because I have fallen in love with these guys (see link).

https://www.elecrow.com/rfm69-shield.html

They are a hair expensive, but the Arduino sketches are SO simple! And they work with 5V Arduinos, so they can drive the big 40A SSR's directly. Most importantly, they work on the 315MHz and 433 MHz RF bands, so you don't need a Wifi router or worry about range issues. Their wireless communication has been reliable enough that I have used them in live theater performances. Just plug in the dedicated RFM69 software libraries, and I was immediately able to code master/slave Arduino sketches using my own dedicated protocol.



My comparison vs. ESP32 using MQTT protocol:

1. Price: ESP32 wins. Half the price.
2. Simplicity: RFM69 shield wins.
3. Compatibility: Depends. RFM69 can run at 5V and drive more hardware directly. However ESP32 might have more software libraries--RFM69 is kind of a proprietary thing.
4. Wireless reliability: RFM69 shield. It's on a lower (configurable) RF band, it comes with an antenna, and it sinks more current. You can handle dropped packets directly in your own Arduino sketches, instead of relying on TCP to do its thing. Except I've never had dropped packets, except due to the power going out.
5. Form factor: ESP32 wins.
6. Power consumption: ESP32. Only matters if you're leaving them on 24/7.