The "no witnesses" rule is a twist I haven't used.
My experience playing Assassin is that it overshadowed other parts of life. Like paying attention in class. Although a very avid gamer, I try to avoid playing games that have negative externalities (other than time consumption and acceptable hardware/software costs, of course). If the game intrudes into the rest of my life, and the intrusion feels negative, CUT IT.
Cambridge rules have a number of places 'Out of Bounds', for "reasons of sanity and safety", which includes all lecture theatres. I think that's a good rule, since lectures don't get disrupted and you can pay attention, knowing you're safe.
Without a "no witness" rule it would have been too easy for the killer. (The other thing I forgot to mention is that you never knew who was after you. You didn't even know who else was playing the game.)
My experience playing Assassin is that it overshadowed other parts of life. Like paying attention in class. Although a very avid gamer, I try to avoid playing games that have negative externalities (other than time consumption and acceptable hardware/software costs, of course). If the game intrudes into the rest of my life, and the intrusion feels negative, CUT IT.