That button cycles through the mission types. Normal, Grid and Linear are available for most public versions of Map Pilot. Linear flight planning is a paid extra so you are shown a popup asking if you want to purchase it, restore a previous purchase, preview what it does (which won't let you take off) or use it in the simulator. If you are just cycling through the modes just hit Preview.
The 'Restore' button is Apple AppStore speak for restoring a purchase that was made previously on the same Apple ID. You can only pay for Map Pilot's extra features one time per Apple ID.