I tested Threads. In my experience, this is how Threads compares to Mastodon:

— The algorithm decides if your content is visible to others. Some content gets zero exposure for reasons which are not transparent.

— Sharing links to other platforms makes the algorithm suppress your content's visibility.

— Slower to use.

— Only one app allowed, and it does not support iPads and other tablets.

— Ads are coming in early 2025.

— You cannot run your own server.

— Your data is mined by Zuckerberg.