Parcel arrived very quickly. All parts work fine, but due to the high flow of the pump (which is good), this would only work for large pots or a pipe restriction needs to be made, otherwise it will overflow before the system can react. Also it will take a lot of trial and error to set the humidity level right for the pump command. Anyway, a good & cheap kit to play with an arduino (that's what I got it for), but probably not viable as a standalone watering set.
It works but the issue is that it works opposite, I want it to works only when the moisture is low and not to detect moisture. You can take from the other output of the relay but then all the system takes a lot of power, can't work from batteries. The price is good.