I have never flown a DA40 or DA42 (plan to have a go one day) but it seems to me that the DA40 and the DA42 are both good 1-person (with occassional 2-person use) VFR/IFR transports.
I don't know how they handle ice but would suspect not very well at all. It's a straight tradeoff between being slippery and not minding being a bit rough
Also I don't think a de-iced (TKS) prop is an option. So, without TKS one would be very limited as to departure and arrival conditions (need to avoid climbing through ice).
The DA42 with full TKS and 1 or 2 people should be a good airways touring plane.
Both have a low wing loading and will get chucked around in turbulence
much more than say a TB20. This is confirmed by pilots.
Every time I speak to somebody who flies them regularly, I keep hearing of a big collection of issues though; the engines (FADEC mostly) and the G1000. But I don't want to spread 2nd hand rumours.
One can read a lot from Diamond's decision to sell mainly the avgas DA40 in the USA, while offering diesel only on the DA42. If there is an engine issue, a DA42 should cope with it without anybody even hearing about it. That's exactly what I would do (can't risk the US market) but potential customers are entitled to working it out for themselves.