Comment by Aaargh20318

They have become popular in the last few years. They are smaller, lighter and thus more portable than traditional mounts. They also don’t need to be balanced with a counter-weight (although they usually allow for a counter weight to increase payload capacity, they don’t need to be perfectly balanced). This all saves in set-up time.

One disadvantage compared to traditional mounts is that they absolutely need guidance, and with a pretty fast guide loop at that (like 0.5s). You can’t do long unguided exposures with a strain wave. But anyone who’s serious about astrophotography is guiding anyway so that’s not really a big deal.