Why Appium

WebDriver JSON wire Protocol

Appium is designed based on webdriver protocol, which is set to become a w3c protocol and aligns with the various frameworks that exist with selenium

Multiple Programming languages

Since webdriver is http over wire, a webdriver compatible language can work with appium. Hence much like that of Selenium, appium client libraries exist for Ruby, Java, Python, PHP, JavaScript and so on. Even with a newer programming language like Go, we have to implement the contract as defined by webdriver protocol and it works.

Release app vs. Debug app

While unit testing tests the paths having access to source code, the end user experience has to be tested with a release app build. Appium works on release app build, hence we have relatively greater confidence on integration and end user test automation scenarios.

Open Source

Since it is open source, there is a huge community supporting and resolving issues. While some might consider this as tough initially, open source with crowd sourcing is the way software world is moving. So it makes sense to invest in such technologies that are flexible at the same time put the decision power in the hands of the developer.