Right then.
I spray undercoated as normal.
This took fine.
I then painted one sample in Coat d'Arms paint.
I then painted the other sample in cheapo crafty paint.
The Coat d'Arms bends with no issues.
Here is the craft paint one:

So, if you are using cheapo craft paint make sure you varnish it.
In the best Ikea traditions I carried on bending and squeezing.
After a while the varnished side started to crack too.
After a very long while so did the Coat d'Arms one.
So… in summary.
If you intend to use them as models and treat them carefully they will be just fine.
If you intend to treat them as stress balls then they will probably end up stressing you out more as they will crack with excessive abuse.
I have glued the Coat d'Arms one to some plasticard with superglue and it has held fast.
It would be a gruntable effort to remove it so that seems good too.