I brought a dedicated iPad
Air 2 with cellar, absolutely love it, I am a bit disappointed though as I must have been reading old threads as ones I were reading didn't recommend the iPad Mini 4 as it was still 'new' they must have been a year old
I think if I was going to buy a dedicated tablet now, I would either go with the Nvida cause of the price for what you get or maybe the iPad mini 4. The iPad
air 2 is great but you get the exact same with the mini 4, so you could get some extra GB for what you paid. Don't get me wrong I love my iPad
Air 2 and after about 10 sessions of 3 batteries, so lasting about 1 hour in total, I have had no problems, I don't use a neckstrap/lanyard, and my arms don't get tired, even though I'm not a particularly strong person but it is just that little to top heavy and only just fits in the tablet holder with a case on, although I guess it is nice to have that extra screen and snug fit.
If you are going to go iPad, go to a store, hold both the iPad mini 4 and
Air 2, and see which you think is best, maybe even take your controller in and see what it feels like (if the security piece doesn't get in the way), because if you're investing that much money in a dedicated tablet you want it to be right.