I too have used soylent for breakfast, for maybe the last 4 or 5 months. And funnily enough, I've gained more weight! Which was the goal for me, as I'm a little underweight and needed to stop skipping breakfast.

I've been using their coffiest drink, and kill two birds with one stone. I do sometimes miss the experience of making my own coffee though, so I may try the powder instead.

I will say though, at the beginning I was not a fan. Bowel movements changed, felt weird and bloated, and so on. But it stabilized after a few weeks.