Risk:
When looking at the risks involved in an action, you've got to look at the probability of the occurrence and the consequences should it happen. The chance of an engine failing is very slim, but should it fail, then the consequences could be catastrophic if the failure is over water. In which case, the risk could be considered as unaceptable.
The effect of the consequences can be reduced with appropriate survival equipment and that is where the questions of whether to, whether not to, and what to buy/take with you just in case makes themselves felt. It also reduces the risk to an acceptable level.
The individual involved is the only one who can make that decision, but he must make it with good pre-knowledge. There’s enough good advice around already on the subject, so I’ll not repeat it here. Suffice to say that I still don’t fly single engine over water unless I really have to.
There is also good advice available on the internet on risk management - it might be worth a look before you next fly over water.........