on smartphone, these office apps offer similar user experience as in Android or iOS apps. On tablet, it is optimized for wide screen. Those who have tablets which supports detachable keyboards, will be able to run either the tablet or desktop version of the office apps. If the device has screen larger than 10 inch, it will show the desktop version by default.
Initially these apps will be available as preview. So, you need to have Windows 10 technical preview to use these apps. Microsoft also confirmed that there will be no more changes in the app except bug fixes.
