That is a smaller filter that they had there. The one I was talking about is probably 3 - 4 times the size of that.

So it was 30-40" long?

It was 10 - 12 inches in diameter and probably 14 inches high. The housing was a monster.

The carbon we use is in small grains or pebbles if you will. the HD carbon is probably one big extruded block. Ten micron you said.
So in our filters, smaller particles will go right through the carbon filter with a low pressure pump.
In a 10 micron carbon block these particles will plug the filter quite quickly.
You would never get the water volume through the block that they are designed to be used for. As well they are designed to be used with house pressure water so you would need a high pressure pump.
Good idea, but I would not use the HD carbon block in the aquarium. As also stated already, we don't know the quality of the carbon.

but it had about 1kg of carbon?

Curious what you really saw, standard cartridges only come in 2.5" & 4.5" diameters.

They had those standard size cartridges there on the shelf also. This thing was a monster; that is what made it attractive. The bigger it is the less often you have to change it.