X1's totally yes, seen everywhere. Anyway to be positive, I thought the IOS 7 issue was fixed now? I used to have an S4 and I've always found them to be reliable...... apart when switching back and forth with a mike on Channel D.
If the question is what is the best controller for Traktor the answer is probably the S4. The new model will eventually prove itself; its a different chip set and I'm sure future versions of traktor will show a bigger gap between the Mk1 & Mk 2.
If you can afford it they newer unit will have greater longevity, mind you I'll say that again in 18 months when the Mk 3 comes out.