GeneXus' Native Mobile generator lets you create applications for Android and iOS using a single, unified model while keeping in mind that the platforms have their differences. Therefore, it generates applications that take into account the best practices and uses of each platform.
For you, as the application developer, it means that the generated application will run on both platforms, but you may have to make some adjustments to make it look and feel exactly as you want on them.
It is important to test the application on both platforms from the start, to avoid detecting these differences at a later stage of the development, where it will probably be more costly to "fix" the application in the platform that was set aside.
In the following links, you will find a list of these known differences. Note that some are structural –that is, these differences are deep into the underlying platform–, and they will probably not be fixed. Other differences can be addressed, and we are working to keep them to a minimum.
Go to http://genexus.com/websac and filter by 'GAPSD' to get a complete list of all differences.
Go to http://genexus.com/releasenotes and filter by 'GAPSD' and GeneXus version or upgrade to get a list of fixes and improvements by versions.