Legal requirements for electronic flight bags like Foreflight or SkyDemon
you actually have two questions here 


  ...for primary flight planning 


EFB's with up to date charts are legal for planning and reference as covered in this question. 

Many EFB's (well at least foreflight that I know of) here in the US allow you to file flight plans, and receive briefs from a weather briefer right in the system.  


  ...and navigation


EFB's are legal for navigation as you would use a map but they are not legal replacements for GPS/AHARS units despite the features they have. Simply put they are not TSO'ed and not legal navigation instruments.

This is also spelled out in the regs directly 


  The EFB system does not replace any system or equipment (e.g.
  navigation, communication, or surveillance system) that is required by
  14 CFR part 91.