My experience says that long term, these relays are unreliable. Two 4 relay boards that control the lights in my shop just failed a few days after each other.
I had two relays fail such that they wouldn’t open. This is a very dangerous scenario because the contacts are no longer being held tightly together and will exhibit higher resistance. Depending on current draw, they may heat up. And indeed, with about 8A of current draw I ended up with discolouration on the board and the relay case.
The 2nd board failed with only a few mA through one of the relays. Being used as a switch to control a heater at 24VAC. After several years of clicking on and off the contacts became intermittent. Typical failure was inability to make contact. Occasionally would not separate. A minor annoyance in this case because nothing in my shop could be damaged by under/over temperature.
Both these symptoms tells me that these cheap relays have very poor contact coating. Indeed if you look at the cost of a decent relay (Omron, etc.) then a single relay is twice the cost of one of these boards.
I am now in the process of designing my own relay board and replacing everything critical with “Songle” printed on it.