I have done a little bit of testing with the device, and based on that I have decided to send it back.
The primary reason for it not being usable in my setup/application is that it can only measure the power on a single phase, because it measures the voltage on the supply terminals. It cannot measure the voltage on other phases, nor use the single phase and “guess” (or be configured for) the phase shift, to estimate power consumption on other phases. It cannot even report the Apparent power, which I think would have been more valuable instead of showing a totally wrong power and power factor.
I guess my expectations for the device were too high
A second thing to be aware of with regards to integration with OH is, that like the Haseman RS-10PM, it is based on the Z-uno development module from Z-wave.me, so a database entry cannot be created (I do have the XML file, and can confirm the manufacturer ID matches Z-wave.me):
Haseman RS-10PM 10 Channel relay module
The seller says that they have verified it working with OpenHAB through the Z-way binding.
Regarding hooking up the device, there are a lot of screw terminals on the device, all numbered, but not labeled regarding where to connect mains and current clamps. The user manual has a drawing regarding which connections to use, but that does not refer to the numbers on the device, so one has to count the screw terminals. Not the most user friendly design, I would say.
Also, a note of caution: The device I received did not have a CE mark. There was a printed copy of the manual (same as the one linked above), but although that states “Conforms to EU regulations: EN55022 EN610006”, the manual does not have a CE mark.
I contacted the seller, who assured me that device was compliant. He said Haseman responded that the CE mark was not on the product “to save the good design”.
I asked the seller since he was in contact with Haseman, if he could request a declaration of conformity, and he actually did, and forwarded it to me. All in all, the seller has been very helpful.