Copper is copper, that's why I find it hard to believe this is a cheap solution just because you are buying it in tube form. Copper is fairly expensive right now per lb, I see no reason why buying it in pipe/tubing form would decrease that price any.
If the stuff mashes down to an acceptable thickness, buying that 1/4" thick piece of bar was obviously overkill. IMO buying tubing and mashing it flat is pretty silly (no offense), just buy flat stock in the thickness you need. It should cost no more than the same amount of copper in tube form (approximately).
Lastly, yes aluminum is not as good of a conductor. But when you can buy a thick piece for cheap, that's nto a big issue. Its pretty easy/cheap to buy a piece thick enough to provide ample current flow with little resistance.