well, it's certainly not correct of the producer to sell this as effective 4K, but the difference is hardly recognisable to the human eye😁

I'm glad you pointed that out! I deliberately bought a native, i.e. real, 4K projector and just paid more. I won't be buying another eshift, it's just a rip-off of customers.

That's certainly a fair point. It's good that you bring it up here. Unfortunately, we also have to accept the manufacturer's 4K in such cases.
However, we are happy to pass the input on to the relevant department.