Agreed on the 10% vs 85% phos acid still get the job done. It’s just a lot cheaper to use 85% since regardless of % the cost is pretty similar, and you won’t need to re-purchase as often.
The lactic flavor component of acidulated malt has never asserted itself in my experience with using it. I am talking a max of 5% acidulated malt in a recipe - higher than that and I would seek an alternate source for lowering pH.