It doesnt have VRM active cooling and these NEED vrm active cooling plus they have components on the left side of the GPU that need cooling too and G12 doesnt cover it. I've used a few of these and I would NEVER not put a heatsink on them. Also if you look at the contact plate there are 3 other areas that it touches the components on the board that the G12 doesnt cover. Would you risk it for £1000?
Also the A bracket on the G12 kit I had doesnt fit the holes. Mine was bought before 2080ti came out so the one listed now might have it but I wasnt going to bother due to the above.