I have 10 of these single relay 12vdc modules (so far). I use them for MANY applications.
In one application, I am powering it from 11.5vdc from a small buck regulator to keep voltage stable.
I am triggering from 11.5vdc through a 68k resistor so, = (about)1.6vdc gives me a high trigger. _|-|_

For solar applications, I have pulled the relay off and used solid state relay! Easy Peasey!
I have also used it to switch my 3000watt power inverter off and on with no relay at all.
Yes, I pulled the relay, lifted pins 3 and 4 of the opto coupler out of the board, soldered wires to them. Inserted wires to COMMON and N.O. pads on the PCB!
The inverter just needs a small make/break, positive action switch to control its power on / power off logic from its' wired factory remote.
The opto couplers output does this perfectly and no relay sucking power.

So, a combination of a programmable comparator and this great little board, I have and ATS (automatic transfer switch) controller for my solar which uses FAR LESS energy (and money) than any commercial unit out there. And it turns the inverter off and on! AND a fully programmable solution to meet my LiFePO4's requirements.
There are no mechanical relays pulling ~100ma each on either board!
When using solar, draining around a quarter amp at 12-13.6 vdc for 12 hours is a lot of waste.

So, these little wonders can be used to drive pretty much anything!
1- Stock relay works.
2- Pull the stock relay and replace with solid state.
3- Pull the stock relay out and lift pins 3 & 4 of opto coupler off the board and you can control logic with said pins!

Triggers off of very low voltage too!

My only CON is the wire capture strips. Really too small and rinky dink.

I recently changed all my lights to ZWave to reduce the WiFi pollution in my home. I needed a ZWave module to use as a trigger for an automation when my Vista20P alarm is tripped but found that no one makes a ZWave module that can be wired directly to my Honeywell Vista20P alarm system. I was able to use this relay module between the alarm and the zwave module. It works great and has been very reliable. Now when my alarm system is tripped all my lights are turned ON.

I got the 24 volt version of this relay board, so I can't attest to the values of the other versions. I took one star off because the product information stated 50mA max current, and my board draws just over 100mA. That spec may have been for a different voltage board. Maybe a 5V board?
The board, by itself, draws about 5mA with no relays active. Each relay coil draws about 24mA; so with all four active it pull just over 100mA.
I'll be powering this with a 24VDC 1-Amp power supply. With with all eight relays active (four on each board), that will use about 20% of the power supply's capacity. Very good for my application.

Edit: Updated to 5-stars. I figured the 50mA max rating was per relay, not 50mA for the board. Then it would be in spec.

Some have called this product less than worthless. That has not been my experience. Mine worked as expected with no issues at all. There are two removable jumpers on the board. I have no idea what they do so I just left them in place as supplied.

The do what they say and seem very reliable. The ability to trigger from low or high inputs is great and you can pair the input with either + or - to make a two wire relay coil. Great item