Daily stand-ups provide zero value in my opinion, asynchronous or not. If one has a blocker then it should be raised to the team in slack/email as soon as you realize you need help from the team. Waiting until daily stand-up doesn't seem sensible to me.
Paying attention to conversations the team is having in slack, the ticket tracker and pull requests gives a much better sense of progress than stand-up in my experience.
So I have mixed feelings. For people who don't want to invest in paying attention to PRs and slack, synchronous stand-up seems to provide more value because they are forced to listen. Personally I'd rather not have stand-up, but if it's required then I'd rather do it asynchronously so it minimizes my time wasted.