We use the TC55's for timing on events. We also have EHS running that locks the device down to itchy fingers and generally works well.
However what caught us out was someone switching off internet time and changing the date.. as you can imagine it really screwed things up for us!! fortunately the issue was spotted and with a bit of a work times corrected.
Begs the question anyway of locking users out from tweaking date / time on the device.