Separate Utilities for Apts - On demand water heaters?

[Sara Bradford]

Hi All, 

I am flipping a bungalow into a purpose-built two apartment home.  To allow for easy separation of utility costs, I'm installing dual HVAC systems, dual hydro panels, and pony meters on the water meter.  This forces me to have two utility rooms (one per unit) and affects my usable real estate inside the house.  Are on-demand water heaters a good investment?  They definitely free up space but what do they provide in terms of efficacy, maintenance hassles, etc... are they worth it??

Thanks!

Sara