I have an iPad mini and it's about a year and a half, when I first got it using NSC was fine.
Problems started after the upgrade to iOS 8, I think it was on iOS 7.1.1 when I got it.
Mine takes ages for pages to load sometimes, other times it's fine.
Logs me out when it feels like it though, especially if I accidentally click on something twice.
I use Twitter a fair bit and never have any problems.