I think Old Fat One has it. I used to regularly fly BPL - IOM in a fixed gear single; I wouldn't do it now. If the engine fails, you are almost certainly going to die. Maybe I'm older and wiser or just seen a bit more over the decades of aviating.
I can't rationalise flying single engine water these days. It goes against my aviation principle of 'always having an out'. If the engine fails over land I'm reasonably confident of living, even maybe walking away. I just can't trust my life to the bag of mechanical bits that comprise an engine and fuel system, knowing that if it fails (and they do as I know from experience!) I'll die.