With a 20 watts amplifier you are not only violating regulations, but more important you are overdriving the radios of clients nearby, which will not be able to establish a stable wireless link. The suggested range of "5,000 meters" of this amplifier with an omnidirectional antenna is marketing speak, it definitely won't work in real life on such distances, especially not b/c the typical clients (laptops, smartphones etc.) will never ever be able to send a WiFi signal back over 5,000 meters due to the limited range of their built-in antennas.

If you plan an outdoor hotspot, deploy several EAP110-Outdoor every 100-150 meters. They will have a typical coverage of 100 to max. 200 meters under ideal conditions and depending on the WiFi mode (b/g/n). Also keep in mind that a single WiFi device - no matter which brand/model - can only supply a limited number of clients (around 20 to 40 clients depending on their usage pattern and the environment).