The ease of use! You can create quiz questions using their templates or you have full freedom with your own custom ones - both look great when displayed/embedded into pages for users without software install (like Apple devices).
There's no free plan so I'm limited how many surveys i may do per month if they don't change this soon though there shouldnt really ever need too much volume anyway at least once setup correctly? It helps us understand our user experience better by creating an A-Z questionnaire survey which we then display publicly via multiple channels like social media posts etc.