I would guess that the low surface area would lead to problems. At first it would cool very well because of the huge thermal mass, but once it reaches thermal equilibrium the cooling would be quite weak.

Do you have any idea how expensive a solid block of copper that big is?

I have a micro ATX case that itself is the cooler. Heatpipes transport the heat to the case walls and they have fins to increase surface area. It can handle up to 65 watt CPUs.

It's not produced anymore. But with all the talk of the Gabecube I've been itching to make a new build with it. Unfortunately I have neither the money or the energy.

Weight, cost, and it's probably not effective for the long haul. The mass of a copper ingot like that will work like a heatsink, but it has a very low surface area for the energy it can absorb. So it'll heat up to a point that is uncomfortable for the CPU, then fail to radiate that energy out to the air effectively.

As a test-bench temporary heatsink, this is actually kind of inspired. No fans, to fussy clips, just stack a copper brick on the CPU, run some benchmarks, and then turn it all off.

Incredibly unwieldy. Real quick estimate of volume puts that at around 1.75kg of copper, so it wouldn't be possible to mount in a vertical PC case orientation (ie the majority of consumer PC cases) without significant (expensive) modifications to both the mobo socket mount and the case, else its weight would snap the motherboard, or just slowly flex it until traces failed.

It may not even be able to be used vertically like that for very long or it will compress and damage the CPU / socket / mobo. Just as an example, the weight limit of the thermal solution (HSF/water chamber heatsink/etc) for socket LGA 1700 is 950g.

My guess is that will only work until it saturates with heat. Some liquid cooling setups are also like that, where the rad isn't capable of dissipating heat fast enough to prevent the whole thing from overheating, but it'll work fine for a while because the loop itself can absorb a bunch of heat before it stops being able to take any more. Then they probably blame the chip maker for running too hot even with liquid cooling when their liquid cooling setup is actually less effective than the stock cooler or their case has horrible airflow and would choke any size or number of rads. But their reservoir acts as a heat buffer, so it takes 30 mins to even realize that, but they've already concluded it works.