The most important thing that I like about them is that their interface is very simple. As an advertiser no regrets. They send good traffic period. However they are not good for absolute targeted converting traffic though. They are basically a brand awareness network which can do wonder.
As a publisher I will say that if you have quality traffic then it is a great network for some passive income. Check for their popup ads and try to avoid them if you could as they can be intrusive to your audience.
Their monetization model works well, but as with any network, testing different formats to balance revenue and user experience is key