I think it's still fine. My experience with many-to-many conversation is that there is always someone whose computer is configured in such a way that it causes everyone's speech to echo and makes it difficult to understand. With a walkie-talkie approach, you bypass this problem entirely.

I think probably the commenter's startup failed because of competition from big hyped, well funded players like Slack. Maybe when the hype settles, they would have a chance. Timing is everything.

Only a handful of lucky few who are well connected don't have to worry about competitors, everyone else needs to assume a competitive landscape full of noise and misinformation.