Copper is actually ~25-250X leas efficient at transferring heat than a heat pipe and convection is hundreds of times more efficient than radiation at transferring heat and the fins on a heat sink would have hundreds of times less surface area for dissipating heat all that is to say this might work but it would be orders of magnitude less efficient than a standard heat sink.
Yeah, but won’t it also be much cheaper than machined, branded stuff?
Considering you can get a half decent tower cooler from aliexpress for like $10, probably not.

Guess we need to do a Cu block vs cheap Ali Express cooler comparison.
Cooling ability for the given workload (probably not much if the customer was satisfied by this one) and noise.

I would say it would have been much better to have the block wider at the top (trapezoidal vertical x-section). That way it could give even better cooling performance.