Given that mixed metals bring about the very real risk of corrosion, and brass/copper have the better thermal properties, I see very little reason to even entertain the thought of aluminum in a loop. What's the point? Save a couple bucks? But then I'm having to buy corrosion inhibitors and change it much more often, while with an all bras/copper loop I can run over a year with nothing but a $1 bottle of distilled + a biocide. Doesn't seem to be much benefit and definitely an increased risk. All brass/copper is practically foolproof.

Swiftech tried a plated aluminum top on a block and that was a miserable failure. They learned and haven't touched that idea since.