The worst thing about balsa core
is that you MUST keep the water
out. If it gets wet it will rot
. So you need to use the correct construction techniques, which does add some hours to your build.
However, Duflex is also available with foam cores. And personally, even if I was building with foam, I'd still take the exact same precautions to keep the core dry.
I've found it to be an excellent material.
The REAL worst thing about it is the cost!
Interestingly, I've recently used some polypropylene honeycomb cored prefab sheet, and IMO it's a vastly inferior product. Panel stiffness is poor, and it's amazingly easy to peel the laminates off the core. OK for furniture, but I wouldn't even consider using it for anything structural.