MTurk has a huge quality problem (around 40% is spam) due to being crowdsourced, and it has a pretty high barrier to entry to get something working well. We hire our own members who we screen for quality for particular tasks, meaning they're fast and high quality. Our API is also much simpler than MTurk's, and we do most of the heavy lifting for you.

There are also lots of types of tasks that MTurk basically can't solve for you (for example, calling a business), that we're working on building high quality solutions to.