I have a Nexus 7, Android, old, now very old.
Android is I gather the best/easiest, you can run another application like Skysafari at the same time. I guess the one pushed to the background still runs so you have the (say) Synscan and Skysafari running together which you need. The iOS units seem to run one or the other but not both.
You need WiFi, GPS, Compass and Accelerometer on the device. Data gets fed from tablet/phone to mount.
Next aspect is that you need a good battery on whatever. They have to remain running, the screen likely therefore has to remain on and you could be out there for a few hours. Also remember that if you are using the system and even if at home you leave the tablet/phone with the mount if you head in for coffee, biscuits, comfort. The wifi connection has to be maintained, otherwise you do the realignment all over again.
If a phone would do then I bought a Xaiomi Redme7 phone. Nice size, good display and inexpensive - think mine was $64 at the time. However I use the Nexus for mount control as it is bigger and I prefer the tablet for the mount and the phone for phone use. But a Redme7 dedicated to a mount and nothing else would not be a bad idea. Just dig out the specification regards memory and battery.