I did destructive tests today by tearing the laminations apart from the foam and here are the results with pictures:
1. Fibreglass facer polyiso foam. Adhesion of both glue lamination and facer is stronger than foam, the separation was in foam. Note the little bumps that are from manufacturing, if there were many smal and deeper penetrations like those, the force to separate the foam from the laminate would have to be greater. Force requried was in the middle of the samples range, but more than with pink foam lamination.

2. Brown paper faced polyiso foam. This one has separated through the paper as being the weakest. Force required was less than all other samples.

3. Torsion box glueup showed the strongest bond to lamination of all due to paper ribs adhesion to the laminate, was actually somewhat difficult to tear apart.
Pink foam lamination strength was in a mid range, slightly weaker than fibreglass faced polyiso foam.

Hope it gives everyone an idea of these polyiso panels. I would consider using FG faced ones. They could be a good solution for
flat panels as they are straight as manufactured, have smooth white surface (no imprints like on pink). I understand why the gentleman who built the "world fastest folding shanty" liked them. The cost in my area is similar as pink foam, considering the fact it will require no sanding and already has one strong layer of fibreglass mat glued. With thickness like 2" they could be good "as is" for a small foamie with corners and joints taped and glued.
That could be a very fast foamie built, but again, for more or less
flat panels. They do have some flex, and light curves are possible with thinner material, or another crazy idea is to delaminate and then laminate the FG mat after the curve is done in place.. don't know, that would another experiment. When teared apart the FG laminate comes off the foam only with elastic deformations, i.e. intact, like a thin Filon, so it could be easily re-glued ... on the small sample I did. The foam in my sample test case separated cleanly which may not be the case with bigger panels.
I will be using the pink foam I already have as I see no big reasons to switch (sell and then buy again

), both materials have their place. Polyiso has better temperature range and was around in sandwiched composites for a while now, but there are some cons too, check MSDS.
Cheers !