72856, welcome to this forum. And soon: welcome to the club of Diamond owners/operators/pilots.
I have flown the clubs DA-40 TDI for about four months and I really like the plane. But we all need to remember that this is the first application of the Thielert diesel in a certificated airplane, and as such, the pilot community in general needs to build experience in handling this kind of engine. Some of us use this forum for exactly that. And eventually, I hope, some of the experience and knowledge that we gained will filter its way through into formal ab-initio pilot training. (Aircraft Technical, for starters.)
One main difference of the Thielert, as compared to the majority of the light aircraft fleet most of us come from, is a total reliance on an electric system, to power the ECUs. Now we can argue about whether this total reliance is good or bad (and we actually do, here on this forum) but at the end of the day we'll just have to accept that a small aircraft will not have the double, triple or more redundancy built-in as the big iron do. So it is very important to learn the POH and know what weaknesses the aircraft has, and what procedures that are out of the ordinary. I, for one, really like the fact that there is no mixture, and more importantly, carb heat to get wrong. (How many pilots have been killed because of carb ice?)
Not discussing an apparent safety issue, as far as I'm concerned, is a greater sin than the safety issue itself. Even if some people voice their opinion a bit loudly. But this whole discussion prompted me to review parts of the DA-40 POH again, to see to what extent the aircraft I fly would be vulnerable to the same thing. I learned something from that and I have a question or two that I will get answered by a bit of experimenting (on the ground) next time I get my hands on the plane.
I suggest you do the same. As soon as your beauty arrives, spend some time experimenting with the ECUs. Particularly try to simulate (e.g. by pulling the circuit breakers) the situation where you have a dual alternator + battery failure and the ECUs need to take over from each other somehow.
The DA-40 is a great plane. The DA-42 should be even better. I really hope you're going to enjoy it!