I was up the Ben couple of months ago with some Hungarian and Polish climbers but due to conditions, we were limited to the tourist track. On reaching the half way lochan, it was whiting out and blowing a hoolie, so we carried on in two groups, my group using map & compass and theirs using GPS.
We all made it okay, although they were somewhat slower than us, and the reason for that became evident when we got home and downloaded their recorded GPS data. It showed them zigzagging their way - all over the place - to the summit, narrowly avoiding the north face - which had a four metre cornice on it - and the treacherous Five Finger gully on the southern side. Visibility down to no more than a few metres, they could easily have fell through a cornice or wandered into 5 finger. As I was on a bearing, straight up and straight down, no narrow misses and considerably less effort, and although I don't have any recorded data to prove that, I'm happy to stick with map and compass, thank you!
In saying that, I do have a GPS, but only ever use it to give me a grid reference... which it is very good at!