It isnt merely ph adjustment... You want some amount of minerals in water for your health, plants, and taste. Changing the PH isnt the concern in most cases, its just part of the result.
All those filters are specifically made for PH adjustment (you are welcome to look at specs). There are bunch of different formulations depends on how much PH adjustment is needed.
RO makes water more acidic. if water was somewhat acidic to start with, it can get more acidic or become corrosive.
Are you sure that it makes it more acidic? AFAIK it only outputs pure H20, should be neutral. If you feed it alkaline water you'll get "more acidic" water, but the other way if you feed it acidic water.
True. But have tasted distilled water? Tastes metalic. Probably just my imagination but I feel like it pulls stuff from the mucous in your mouth and tastes like blood.
RO makes water more acidic. if water was somewhat acidic to start with, it can get more acidic or become corrosive.