Twins versus singles - now here is an old chestnut.
The first comment people usually make is that twins are less safe. That statement is wholly erroneous without qualification. Twins are, on the whole, used for quite different mission profiles. Far more poor weather sectors are flown in twins - because on the whole they can cope with worse weather.. The general statistics also pay regard to the experience over the last forty years. Particularly in the States it dawned many years ago that twins were susceptible to asymmetric accidents in particular, and accidents in general with pilots flying in conditions for which they had inadequate training. Twin training has improved enormously in that time and even more importantly the insurance companies had made it increasingly difficult for inadequately trained pilots to find cover. There is no evidence in the current environment that twins are less safe, and if you take account of the mission profiles flown they are more safe than singles.
There are many similarities with high performance singles. In the early years the accident rate in the Cirrus was far higher than you would have expected. Pilots with inadequate training were lulled into a false sense of security by the fancy avionics, performance and promise of a state girdling light single. Of course the Cirrus was still a single, and with its added performance less forgiving in poorly trained hands than a Cherokee. The training has improved enormously, and in the States at least the insurance companies have set the standard. The accident rate is probably now better than that for other singles. (Probably because statistically it is still early days).
It is true that the climb performance of many twins on a single engine is poor or almost non existent. It is equally true that for many twins the climb performance is acceptable. How many critical engine failures do you read about each year in the UK? Of these how many singles do well in terms of avoiding injuries?
I have quite a few hours on 42s. An engine failure immediately after take off before you have cleaned up the undercarriage is an issue, but not unmanageable. An engine failure a few moments later is also an issue but far less of one. As long as you are on the ball the aircraft continues to climb quite nicely even at MAUTW - I have flown singles that barely do much better. An engine failure in the cruise is a complete non event. I had one last year. If I had to we would have flown on for as long as necessary. Personally I don’t subscribe to the school that a failure is anything other than an emergency and I don’t subscribe to flying home on one engine - but if there is no alternative one could and would. Had I been in a single which might easily have developed exactly the same fault I would have landed in a field. With luck I would not have been uninjured, with a whole lot more luck the aircraft might have survived without a reasonable amount of damage, but probably not.
In the last two weeks two Cirrus have sadly been lost due potentially to engine failures. In once case the pilot lost his life, in the other one crew member escaped without injury, the other was injured. The aircraft is a write off. In a twin with a current pilot if the accidents were caused by an engine failure neither the aircraft or crew would have suffered any consequence.
On the whole twins carry more weight. On the whole twins are better equipped to cope with weather. That does not mean to say singles cannot be so equipped but in reality few are. Twins will typically be certified for flight in known icing. Twins will typically have boots rather than fluid which is only “lifed” for as long as the fluid in the reservoir lasts. Twins on the whole have significantly higher cross wind limits and are more stable both on the approach and in flight. If you care to fly an Aztec in turbulence, and a single in the same conditions you may well wonder why the passengers are throwing up in the single. Twins on the whole have significantly more redundancy. Twins are on the whole are faster and perform significantly better - at least when both engines are working!
Some modern high performance singles attempt to emulate twins on some of these counts but none emulate twins on all counts.
In defence of twins you therefore get a great deal more than just an extra engine. On the whole you get better performance, greater comfort, more redundancy, improved all weather capability and, with a current and well trained pilot, more safety.
One last thing - you worry a whole lot less. I know engine failures are remarkably rare. I know the engine doesn’t know it is over the sea or the Alps or it is night or there is a 800 foot base. Never the less it still doesn’t stop me worrying in a single half way to the CI in the middle of February with a cold 5 foot swell beneath that an engine failure will definitely ruin my day. I would only fly twins if safety was the sole issue - as it is singles are good fun to fly for other reasons, and a whole lot less expensive.
So to answer your question Diamond were brave enough to try and prove there was a market for a modern twin - inspite of the ill informed bad publicity with which they had to contend - I think they have been very successful in that regard if let down by the choice of engine. Tecnam will hopefully apply the same formula to powering a mdern twin with a much cheaper Rotax already used in loads of non certified aircraft. They apparently have a pretty good order book. I hope others try.