And since they said that it uses 10-20% the water of a standard shower head...
A modern shower head uses about 2gpm, so we are talking about 0.2 to 0.4gpm. That would give us a pressure of about 7500 to 15000psi using your equation.
That sounds like the worst case to me. They are doing their demos with 7500 psi from an outboard pump and thinking that it's going to be a minor detail that can be worked out after the kickstarter succeeds to generate a workable pressure from 15A 120v.
If they told us the pressure they're using for their demos, some smarty with a slide-rule might call them on getting that from a normal wall outlet.
At least in the UK, Her Majesties Customs and Excise tried to measure it in biscuits (which require 17.5% greater cutting force than cakes), but Mcvities prevailed in the courts.
A modern shower head uses about 2gpm, so we are talking about 0.2 to 0.4gpm. That would give us a pressure of about 7500 to 15000psi using your equation.