Yep I have a few of these which are very similar (but have two relays). These can both be re-programmed with your own firmware, i.e. Homie, and thus allow very easy integration with openHAB.
I have yet to put mine into use but have tested the relays and they work well.
To update this thread a little, I got a Wemos D1 Mini which Iāve been playing with.
I originally experimented with Homie which is configured from the Arduino environment. The developer Marvin Roger is very helpful, and on the main Homie thread on this forum heās provided a way of working around the current 5 node limit which will be removed in the next version. As a package Homie works well, and allows the sketch running on the ESP to be used for simple rules such as āif this input, send that outputā as well as interface with Openhab via MQTT.
Right now by way of a contrast Iām trying ESP Easy, which after the original Flash, is configured with a simple web interface, it exposes its basic I/O over MQTT which can be used with Openhab, this seems to be a simpler solution for those that just want to expose a bunch of devices to Openhab over MQTT as it doesnāt require any Arduino Sketch knowledge.
This ESP will be used to control 6 relays, and provide inputs for at least one 1-Wire temperature sensor and an analogue wind sensor, the only issue Iāve found so far with ESP Easy is the topic length in the command topic only seems to work at one deep. For example
Topic āMySensor/ā works
Topic āMySensor/Basement/ā doesnāt.
The full topic to access the GPIO Pins is:
āMySensor/gpio/14ā with a message of either ā1ā or ā0ā depending on whether 0V or 3.3V is wanted on the GPIO Pin.
The ESP Easy wiki mentions instability when controlling items but doesnāt mention whether this extends to simple relays so Iāll update the thread when my AliExpress $2 relay boards arrive and I can test it properly. For now I have 2 single relays, an LED, a relay shield and a 1-wire probe hanging off it that Iām keeping an eye on. Iām also pinging it every 10 seconds to check for wifi dropouts. Will update this if any of them fail.
I am also using ESP Easy on two Eco Plugs that I picked up for $8 at Home Depot after Christmas. It has been working well. The only āissueā I have run into so far is when my MQTT server was down for a couple days in an attempt to migrate my server from ESXi to Proxmox. The physical button would become unresponsive for several seconds when, Iām assuming, the device was attempting to connect back up with the server. I really like the web interface and OTA updates though so itās easy to change if you repurpose a device. Iād like to find something similar for Arduino.
I am torn when it comes to DIY control of high voltage. I donāt doubt my own ability, but Iām a bit apprehensive about the quality of the cheap components. More importantly, Iām not sure itās worth the risk in event that the worst happens. If my house burnt down, even for an unrelated reason, and insurance denied a claim because of some DIY controller, then Iāve defeated myself in my quest for saving money.
Those Sonoff switches would be great. A nice packaging for barely more (or less even) than you could do it yourself. They donāt have any kind of UL listing or equivalent that Iām aware of though.
Iām curious how those of you that have done DIY high voltage equipment feel about this.
I stick to off the shelf certified sockets wherever possible, and then add inline fuses if appropriate. Iād rather blow a 650mA fuse than rely on a 15/20A breaker back at the mains board.
Really? Are you using nails instead of fuses 
.
hahahaha, 650mA 
original edited for those following later
To update this thread, for those following on, I ended up:
I purchased 2 x Wemos D1Miniās, I flashed both with ESPEasy, one had a boot loop problem and was refunded, the other is connected to a 4 port relay board, the mains feeds to the lighs is diverted through the relays, and I also added a couple of 1-Wire Sensors as my 1-Wire dongle used elsewhere was throwing the occasional read error. The ESP is also connected to 4 light switches with pull ups to 3.3V, and the light switches pull the lines back down to 0V when operated. The relays switch the mains feeds to the lights which are diverted away from the switches which are low voltage only.
I use ESPEasy to report the relay status via MQTT back to OH and the ESP runs a set of simple rules that flips the state of the relay whenever a switch is operated.
This setup means OH knows the state of the relays and restores it if the ESP restarts, I can now operate the lights from either the switches or OH, and in OH the Switch items always reflect the light state.
I had to buffer D8(GPIO15) with a 10K Resistor and a BC547 as the relays hold it high which stops the ESP from rebooting. Also D3(GPIO0) and D4(GPIO2) have 10K pullups so they have to be used to feed the active low relays to prevent reboot problems which happen if they are pulled to 0V when rebooted.
Total cost for Wemos D1Mini & 4 Port Optically Isolated Relay board is $8 USD, and its powered from an iPhone charger with an extra Tantulum Capacitor across the 5V rail. Iām fortunate as I have the time and knowledge to do all this stuff, so my solution wonāt suit all.
RATHER OBVIOUSLY ONLY WORK WITH MAINS IF YOU KNOW EXACTLY WHAT YOU ARE DOING AND ARE ALLOWED TO DO SO IN YOUR LOCATION.