Thanks for posting the tests. Did you varnish your models afterwards to stop it from rubbing off further?
Hi Pil!
No I have not yet sealed the models. They are actually quit dry to the touch and do not rub off at all.
Feels like normal paint jobs

I would assume that you could actually handle them quite a bit without having the color rub off but as the paint contains no materiel to chemically bond the paint materiel permanently to the subject, there is always the risk of rubbing off or dissolving if coming in contact with liquids.
So to be on the save side, it is best to seal them. - and mind you that it has to be a spray seal as a brush on sealer might dissolve the paint again.

regards
Thomas