Unless you have really soft water you'll only need to acidify the mash.. and you'll typically only have to do this when you're using lighter colored grains. So, as long as you don't live in Pilsen, don't use a water softner, reverse osmosis, or distilled water all you'll probably need is some gypsum to acidify things and it's a heck of a lot cheaper than that 5.2 stuff. Aside from PH's effect on enzmatic activity (and thus efficiency and sugar profile) it also directly affects the likelyhood of tannin extraction - this is why we stop sparging when the PH of the runoff hits 6... and why some acidify the sparge water.
Minerals create a PH buffering capacity - this is why the acidifying effect of the malt sometimes isn't enough to lower the mash PH into the 5.2-5.3 range when the brewer has very hard water. Of course, if you use brewing salts (i.e. baking soda, epsom salt, and gypsum) to tinker with the mash PH you'll need a PH meter to make sure you hit the right PH - those papers get old fast.
I think the 5.2 stuff is marketed as a cure all (and an expensive one to boot).. I do not think it's worthless but I do think a little bit of water chemistry knowledge coupled with some very inexpensive brewing salts will better serve the homebrewer.
My .02