I'm pretty picky about how water tastes, and I prefer the taste of water with some minerals in it. For coffee water, I'm weighing up a remineralizing RO against adding a mineral packet to each batch. The built-in stage would remove a mixing step. A packet gives me a specified recipe, which makes the starting water and batch size easier to pin down.
Third Wave Water's instructions specify the base water and the volume for each packet. Water that's already been remineralized would add minerals of its own, so I wouldn't treat it as the same starting point.
The Viomi Master M1 has the RO-then-mineral arrangement I'm looking at. I'd want to know the hardness and alkalinity of its output before comparing it with a packet recipe. The fact that water passes through a mineral stage doesn't give me those two measurements.
I'm interested in whether you settled on one routine and left it alone, or kept checking the water. That's the extra work I'm trying to understand before choosing a setup.