As per Philippe:
“The biggest roadblocks at this point are performance and memory consumption. Simulating a full scale Earth with accurate topography and 15m satellite imagery takes a lot of memory (RAM) which can cause the app to crash after a little while if we are not careful (the app itself doesn’t crash, the OS automatically kills apps that use too much memory). We currently still have a lot of issues on devices that have less than 2GB or RAM but are working hard to solve those.
About performance, there are still many optimizations we need to do, especially on Android. Recent iOS devices (< 2 years old) seem to be very stable but we still have to improve some bits to make sure we don’t kill your battery. :)”
So something recent with 2gb of ram or more. More info is in the “when is the update” thread I linked above. It shows different optimization levels. If you want the best quality I’d stick to a good tablet. Personally I’d get the iPad Pro if you’re looking for a big screen but it all depends on you and your preferences.