Review on 🔌 MakerFocus Raspberry Pi Expansion Board: 4-Channel Relay Module for Raspberry Pi 4B/3B+/3B/2B - No Programming or Programmable Options by Scott Welch

I like the module and it looks high quality - not sure how much current the relays can handle as they are physically small. Modules are stacked and programmed over the I2C bus. I don't know if the RPi can supply enough power to run 16 relays (4 stacked), but there is an option for an external power supply. My only concern is that the provided API only allows the relay to switch one at a time. My use requires two relays to switch simultaneously, so the module will not work for this application - if simple switching is required, this is a good solution.