MySQL Enterprise Monitor is the best way to monitor MySQL databases from a single to multiple instances on your network or in the cloud. Period. This, to me at least, is the core tool that comes with an Enterprise Subscription. You can use it to monitor the free Community Edition of the MySQL Server but you do need to purchase the subscription.
MEM monitors of MySQL instances (and their hosts), gives notification of potential issues or problems, and it will also provide advice on how to correct issues.
The MySQL Enterprise Monitor Agent monitors the MySQL server, including checking the server accessibility, configuration, obtains the server ID, and the environment to enable collecting more detailed information. In addition to the information accessible by accessing variable and configuration information within the server, other configuration parameters, such as the replication topology, are also collected from the server.
The collected data is sent to MySQL Enterprise Service Manager for analysis and presentation. The MySQL Enterprise Service Manager analyzes, stores and presents the data collected by the agent. And you can view all this information from a web browser with an easy to use and understand interface. And yes, there are demos https://www.mysql.com/products/enterprise/demo.html
Improve Your Queries
MEM does more than just watch the server. The MySQL Enterprise Monitor Proxy and Aggregator intercepts queries as they are transmitted from client applications to the monitored MySQL instance and transmits them to the MySQL Enterprise Service Manager for analysis by the Query Analyzer.
This data is from Performance Schema, rather than at the wire protocol to provide data about what the statements do to generate their result sets that other sources cannot provide such as table lock time, how many rows were examined versus returned, how many temporary tables were created ( and whether any were created on disk), whether range scans were done, whether sorting happened, how many rows were sorted, and what form the sort took. You also get histograms of response times, standard deviation of response times, and other valuable information.