Based on my experience, tools like ZeroIn work much better compared to the databases you see here. Databases get outdated frequently and its not easy refreshing them at regular intervals and Useartemis and leadrocks both seem to have a lot of outdated data. Whereas, ZeroIn is pretty much finding data for you in real time, which ensures a lot of valid emails. Downside to it is that you might not find emails for every prospect. Personally I'm loving using zeroin and have bought more than 30 codes in total for my whole team.