Cottonwood burns fast, lots of ash, I use it when someone has me cut and haul it from their yard or something, but I don't look for it otherwise. Blue spruce I have a lot of on my 12 acres, have cut a dozen or big ones when killed by budworm. The rounds near the base, in this area of the world, are typically 25 to 32 inches diameter for a hundred-footer or taller. Naturally, this makes very heavy rounds, even dead and dry. I no longer wrestle them up into my truck bed via ramp, I section them up to where I can pick up the pieces. [Noodle making] It burns fine, though it is nothing like hardwood. It is better firewood than cottonwood, not as good as ponderosa or lodgepole, in my opinion. But I'd sure take it if I were you, particularly as the guy is willing to deal with the trillion smaller branches they have and which are a bear to haul off and handle.
I don't have a splitter, do it by maul and axe. The blue spruce, unless really seasoned, can be a real job to split by hand. I often have to hammer the maul through the splits with a sledge. It is a real workout. If it's seasoned, and has been cut into rounds a while, it will have begun to check pretty well and is much easier to split.
