RO water is demineralized and the pH is impacted. It is not a healthy drinking water outside of occasional use. It is also not appetizing and thus it's easy to become dehydrated.
After years of RO water I switched to spring water due to health issues and I will never look back.
Of course, it is insanely expensive to drink 3L of spring water and so frustrating to not have unpoisoned water from the tap.
There are certain models which have a sixth stage to remineralize the water and balance the pH.
Also relying on municipal water for mineralization is a bad argument. The minerals in water supplies is highly localized, or drinking tap water could leave you deficient in one or more minerals depending just depending on where you live.
It won't be used for showering, bathing, flushing toilets, washing clothes, washing dishes, watering plants, washing cars, filling pools, or other outdoor water usage. How much does it increase a household's water usage?
I think that's improved, at least according to product literature (I haven't tested it myself), however:
The latest generation of small under-sink reverse osmosis filters claim to waste only 1 gallon for every 2 gallons of usable water. Still bad but much better than before.