I recently bought the 25-KAS I can say they're great. The beauty of having a closed cup is that they provide some passive noise reduction. So if the batteries run out, you still get some relief from the noise. It isn't that noticeable at FL390 but at FL250 it makes a difference. (the Passive NR, the ANR is very obvious at all flight levels)
You don't need the "S" version unless you have a stereo jack. I bought it just because I could. I don't need it but you never know...
