I noticed the broken demo also. That alone screams RED FLAG in regard to the wp-quiz plugin. If you won't work on their own site why should we think it will work on ours? I installed the wp-quiz plugin on my site and found the Multiple pages setting also does not work. Whew! That was a close one as I almost purchased the broken plugin before I found out that support is lacking, slow or none existent. Seems they don't want to answer any pre-sale questions and seem to block potential buyers from seeing all the paid for pro plugin problems. However they cannot hide them on the Wordpress website plugin reviews which are not looking very good at all. On my site as soon as you enable the Multiple Pages feature it let's you answer one question then when you click [Continue] button the CSS animation gets stuck in an endless loop and NEVER continues to the next question. Furthermore it does not give you the option to chose NO animation so you are stuck in this endless loop forever. You can see the problem here=>>
To be fair it could be a plugin conflict but I don't see a page where known issues are listed or maybe they are also hiding that from presales questions. Something is just not right here. For the amount of money they are asking I expect full transparency, honesty and real support. If they step up to plate I will change my one star rating and negative reviews across the internet. But until then we have to make our decisions based on unresolved issues, all the 1 star reviews and slow or poor support if it at all exists for potential customers.