Great advice, thanks all. Decided to get an S100 + Canon housing, no strobe for this trip. Since it's been a while since the last dive I'll be leaving it in the hotel for at least the first boat dive and will practice snorkelling with it. If I feel like I'm confident and able enough to use it I might consider it on the next set of dives. Likely to be doing a number of pretty shallow ones too so I'll maybe use it for those and leave it at home for anything deeper.