You drop a hydrocal piece and you almost certainly break it. Zero flexibility. Resin is much more forgiving when mishandled. More flexible.
Generally so, but older resin will shatter like a ceramic on a hard floor - best to not drop stuff and not to test either out, 
Resin generally weighs less by volume.
True!
Large hydrocal pieces (say 12 X 24 inches) are best cut very slowly with a hsnd saw to prevent chipping/breakage.
I use a hack saw blade w/o the handle to cut hydrocal castings.
Resin can be easily cut with care on a radial arm saw with a 160-200 tooth blade.
Or a band saw, or a hack saw, or a razor saw or .......lots of options!
Hydrocal can be easily repaired using spackling paste.
Or more hydrocal and it's also easily glued back together with Carpenter's glue.
I have used both resin and hydrocal for large building fronts and am happy with both, but my preference would be resin.
Unless it was stone, I'm with the resin option, too.
