I bought 2 4 channel relays and each have a bad relay. One the relay clicks delayed but no switching (NO -> Common). The other had a bad control circuit on one relay (no click). I run these relays on a regulated 5.0v power supply that is closely monitored.. I have 2 other (4 channel relays) that work fine, no issues.

Update: I did some testing with the replacement relays, had the same issues and discovered they are not actually bad. Not all optocouplers are 3.3v friendly, even within the same set of 4 relays. I have bought several of these sets from other vendors and they all were 3.3v friendly and worked well with a Raspberry PI. These are not the same as the others even though they appear to be. As for what they do, they work with 5v ONLY when you use High triggering. Low triggering will work with 3.3v just fine.

The relays that are used in these are awesome relays. I have used them for a 120v 1HP pool pump project and DC switching with great success. One is over a year old and it is the hardest stressed running the pool pump. I have not had a single relay go bad on me yet. As long as they work out of the box, they work for a long time. (Just over a year using them).

As for these use with Raspberry Pi, You will need 5v control and that means using a voltage shifter (available on Amazon) or use Low Triggering or look for other relays that look like these and are 3.3 friendly.. Some relays within the 4 group will work with 3.3v, good chance at least 1 will not.

I am currently using this to switch my spindle on and off on a CNC machine I made. I 3D printed a DIN rail bracket to mount it to and the wiring is pretty straight forward. Works as advertised and I am very pleased with it for the price point.

You need to be careful when buying electronics online they are not all made equal. This item is built strong and can handle the ratings that it claims many out there are built very cheap and can be a hazard to work with.

Draws 2.19 mA from a 3.3 vdc command source to activate the relay.
Draws 169 mA from the 5.0 vdc power supply to activate the relay.
Draws 3.5 mA from the 5.0 vdc power supply when no voltage is supplied to the command line.

I will be using it NC to switch 350 watt 24 vdc source to Ender 3 Pro via Octoprint with PSU Control plugin.

I have purchased and included ten (10) of these in a solar project. Knock on wood, I have had great success, as each relay has performed as expected. What's more, the board is beautifully laid out with a legend printed right on the board. Only mistake I made was to use 5v from my Arduino project to power the relays, which draws more power than the Arduino board can handle. This was my bad, and once I supplied 5v from an independent power source, specifically for powering the relay(s), all was good. What's more, unlike many Internet of Things accessories, these relays have excellent input and output connectors, that allow me to use high quality (thicker) wire than others. Finally, the board is supplied with helpful relays, one of which indicates power to the board / relays, and then one for each relay, to indicate the relay is energized. I will buy more and do recommend to friends and colleagues!