The UI is easy to navigate, and results are typically delivered faster than quoted. The feedback received from these tests has been instrumental in refining our messaging. Recently, I upgraded to use audience segmentation and think it was absolutely worth it to get an audience within my niche. Their webinars are spot on too, very actionable.
Easiness and speed. It's too easy to use, you don't need extra guidance to create your tests, and you get your responses quickly. It's the best tool to validate messaging I've ever used.
Agility in delivering results, the ease of setting up a test, and the audience quality (especially for C-level positions), which is difficult to talk to normally.