Skyview VS iFly720?
Not sure this is actually the right question.
Experimental aircraft need a primary flight display that I believe needs to be engineered specifically to be a primary flight display (PDF). DynonAvionics, MGL, Garmin, TruTrak, etc. make units that meet this need. The box right in front of you should be a dedicated unit designed from the ground up for flight.
You second unit is a different matter!
The tablet will follow Moore's Law, and will double in performance every 18 months, with a steady or dropping price tag. Because these are general purpose computers, with sales in the millions, R&D cost is not a limiting factor. Specialized hardware can not change like that.
As the hardware advances, the software makers struggle to keep up and keep competitive. Add new technologies that are maturing like bluetooth communication, solid state memory and display advances, and the tablets will far outpace your PFD at a fraction of the cost. Advanced software and external ADAHRS devices will make a tablet a more than adequate backup. MAYBE even BETTER than your three years old PFD.
In my installation, I'm going with Skyview as a primary, and a panel mount tablet that I can throw away every three years. I'll buy the remote ADAHRS, and get an easy to update system that will stay modern at a reasonable price over many years.
CC