I've had a cambium on my commuter for a couple of months now and quite like it. It has a nice amount of give to smooth out the smaller bumps (though not as much as the sprung Brooks Flyer it replaced), I don't have to worry about covering it in the rain, I like the slight texture as I don't slide around on the seat unless I want to, and it seems to have a flatter profile than the leather Brooks seats I've had/tried (which makes it more comfortable for me).
As for being a brick, it is a little less than 0.4% of the total weight of me and the bike. Switching to a lighter saddle might save me 0.2% of the total weight, but I probably wouldn't notice the difference to be honest. What I would notice is if the lighter seat was not as comfortable.