the DIN is the point though. if he's riding the jester about an 8 he is on the verge of the minimum that the binding should be rode on, yes the binding should technically release at the same torque as a lower range binding, set at the same din, but as a general rule you dont really want to be riding in the top or bottom 2 of the range.
you mentioned the strength, the material choices will be based around the stresses which somebody, (who is the correct weight for the binding,) will put on a binding. i.e. somebody with more weight will require more torque to eject the binding putting a greater stress on the materials. with the OPs weight the extra binding weight to make it stronger would be a waste of money.
I said to pick the griffon because the din range is more appropriate for his weight, the minimum recommended weight, by marker for the jester is 60kg and OP is barely that. for the extra strength the extra binding weight/cost isnt worth it for the OP
with the lifetime in mind, if he is only riding it 30 or so days a year its unlikely he is going to thrash the binding into breaking before he decides he wants new bindings for a different pair of skis.
If getting more metal components is something bothering him im sure there are bindings with more metal out there, for his weight, and i would recommend having a look at some of them as marker is not the be all and end all of bindings.