This was my personal experience with Zeropark. Lost a lot of money and made nothing back.
Their traffic is real for sure but conversion is limited to only a few zone. And to get traffic from these zone, it cause a lot of money thus rendering the campaign with losses. All those testing of zones are just bullshjt and a way to get money off your pocket legitimately. They will claim that you can choose cpa bidding but if you use that mode, chances are that you will receive close to zero traffic after they approve you for cpa bidding.
When you complain they will ask you to raise the cpa bid price. Again you will be astonished that it results in campaign losses once you start to raise the price in a.bid to get traffic.
Dont believe me? Try it on your own.