Mode S at TC is worth its weight in gold IMHO. Certainly an extra safety net when you can see what FL is selected as it helps to avoid potential level busts/losses of separation.
Had a situation a while back where a pilot was heading 312deg. On initial contact, told him to "turn right 3 deg, heading 315deg". Bit of stunned silence ensued....then he asks me if I can see his heading. As it was a nightshift I had time to explain to him all the virtues of Mode S and what data was available...
"WOW" says pilot....
"I know" says me, "I can tell if your telling porkies on your speed restrictions"
"Bugger" sniggers pilot.
Good banter, kept me smiling for a while
MODE S....TOP KIT
Spamcan