As far as I am comcerned ther is no question, if you value saftey over everything else, go for twins.
So if thats the case why does not evryone go for them.
Well their are a number of cons,
While they dont use twice the fuel the extra drag of the drive makes you loose about 25% of the extra power, i.e. a twin 50's will give you the same power as a 75hp single.
The cost of buying and servicing is higher
To make full use you need twin redundent systems, fuel, battery etc.
Given this you need to ask yourself the following questions.
How far do I go solo, would a 6HP aux get me home?.
Do i usually travel as a group
If I cant get home how close is help
If you do have to get home on a aux, are you set up to spend say 10-20 hours in a open boat?. Dont forget 1 hour at 40Kts is 10 hours at 4Kts, assuming their is no tide etc
But in real terms most people would be able to get a tow.
These days outboards are very relieable and if well looked after and serviced should ramain so, but one is better then two IF set up right.
Answer yourself the above question and then decide. If in dought and you can afford it go for twins, it the safe descision.