There are several ways to control ISO, a popular way is with the command wheel in EasyISO mode, and I set my Fn button to switch between AutoISO and fixed. I hardly ever used the button on the back for ISO and instead used the EasyISO wheel. My experience with that style body has been the D7000. The U1 and U2 user banks worked for me by setting U1 for non-flash subjects and U2 for manual exposure, fixed ISO and shutter for flash. That way I could shoot all night in mixed light events without using the rear left buttons.
You can press the - button in review mode until a grid of small thumbnails are seen and shift through the photo up and down columns and along rows very quickly but very seldom used the review screen to look at an image after it was taken unless someone wanted to see their photo. KatzEye does not have a focusing screen yet for the D600, the last time I checked but surely they will. I liked the small size and features of the D7000 which shares the same planform with the slightly larger D600 and found it just as responsive to change settings if I plan out practical use of of the feature to remap buttons as on my D800 which has more dedicated buttons with more space to lay them out. All of them surely benefit from using the optional grip for better handholding. Stan St Petersburg Russia