I have recently found the quick hardening nature of Hydraulic cement
to be very useful for patching things like my fieldstone fuoundation
in areas where a regular mortar mix or concrete would tend to slide
off.

The quick setting nature allows me to shape it in ways that either I
couldn't do with ordinary mortar or concrete or that would require
complex forms.

Other than the expense of hydraulic cement, is this a "legitimate" use
or is hydraulic cement deficient to mortar or cement in structural
ways that I will come to regret? (note none of my uses require
extremely high compression or strength ratings)

If this is a proper use, then I must say that hydraulic cement is a
great short-cut solution for small handyman repairs.

Thanks