The thing about Twitter is that it really lacks a lot of the features you'd expect from a true Mastodon replacement.
For example, there's no way to edit your toots (which they, confusingly call "tweets"—let's face it, it's a bit of a silly name that's difficult to take seriously).
"Tweets" can't be covered by a content warning. There's no way to let the poster know you like their tweet without also sharing it, and no bookmark feature.
There's no way to set up your own instance, and you're basically stuck on a single instance of Twitter. That means there's no community moderators you can reach out to to quickly resolve issues. Also, you can't de-federate instances with a lot of problematic content.
It also doesn't Integrate with other fediverse platforms, and I couldn't find the option to turn the ads off.
Really, Twitter has made a good start, but it will need to add a lot of additional features before it gets to the point where it becomes a true Mastodon replacement for most users.