The good ones actually have an additional filter that remineralizes the water. Which is great, IMO because this also keeps the taste of the water consistent and you don’t have any funky flavors from the mineral content of your area.

There is some literature out there about pure RO water not being great for you.

My anecdote: I have been purchasing RO water from the local grocery store for quite some time because I dislike the taste of my tap water after softening. For a long while I drank the RO water as-is. When I started adding mineral drops to the water, I felt a lot better.

it doesn't remove all minerals. Flouride isn't removed, unless the unit also has an alumina filter.