John, that sounds reasonable when you're using a tablet temporarily and as a supplement to the airplane's own instruments. But as soon as you think about installing a device in an airplane even semi-permanently, then having to "cover the tablet screen... to keep it from overheating" becomes unacceptable. It's more a toy than a serious instrument. That's what's so good about the 740/740b. It's a serious, reliable device. You turn it on and it works all day in direct sunlight and never gets washed out or goes dark. It's dedicated to aviation.
On the other hand, Adventure Pilot's email this morning (Monday, the 19th) hints at several new and exciting developments--the most interesting of which is a HUD. If that can display iFly GPS or EFB effectively, it might truly change AP's game and supplant tablets as the primary display device.