I think we have given this one a good airing in the past. But as a quick note.
1. Twins will always provide better stability to the vessel. Look at a transom elevation put a single on and compare the fulcrum to a single.
2. For performance the single will give better.
3. Set up well, a pair of twins WILL NOT use more fuel than a single.
4. If one engine goes down the second may well not get the vessel on the plane but should provide a good 10knots which is much better than a 5hp aux which will give only a couple of knots.
5. The manouverabilty on a well set up pair of twins is superb when used correctly.
6. Twins may be seen as a lux but for those who have used the set up they will never go back to a single.
7. Agreed that it is the servicing of two engines but with a good dealer they will price according to volume.
And on the point of twins
1. All of our vsls are twins.
2. We have 6 kids - including two sets of twins so a tad of bias !!