I have a Samsung Galaxy Tab4, in 8" and 10" that I use for my Spark and P3S. I tend to use the 10" version with my P3S, mostly due to the heft of a tablet that size fixed to the Spark controller (even an 8" is pretty huge compared to a phone). Both run on Android Marshmallow, and the only issue I've had on either is having to restart GO/GO4 a time or two to get rid of any video lag (which sometimes runs into several seconds on either uav). Once things are up and running smooth, they work great throughout the flight.
I bought both of the tablets used at a local EZ Pawn... they literally had a couple hundred in stock. Everything from iPads to really cheap (ie: crappy and won't work with either GO app). I gave a $100 for the 10", and about $80 for the 8". If you shop there, get their addon return policy for a few bucks more... def worth it if there are issues. Certainly saved me some money vs pulling the trigger on something new, that may or may not work with the apps to start with.
Though I have the bigger tablets available, I still make most of my Spark flights with a Galaxy Amp Prime. Again, that's due to the heft and added hassle to setup the mount and such.
Sunscreen wise, I fabricated one for the 8" tablet out of a harbor freight pneumatic nail gun box that wraps around the sides. I use flip covers on both tablets and left simple tabs hanging off the sun screen that tuck in between the tablet and cover back (2 on the back, 1 on each side panel). It works great, and some black paint made it look pretty decent!
