Cassini operated this way. I mean, it wasnt designed to operate this way (see my Haynes Cassini-Huygens Owners Workshop Manual) - it had a regulator, but somehow the regulator stuck open with a high leak rate - not enough to pop the propellant tank right away, thankfully, so the operators were able to close the upstream latch valve (which turned out to have a rather lower leak rate than specc'd, fortunately) and burped it later to maintain the ullage pressure as the fuel depleted. Sounds like Peregrine jumped to that approach - higher risk, but simpler/lighter

Biprops are hard to get right - a lot of failures/anomalies attributable to this piece of the system - Mars Observer, Akatsuki, Cassini, JUNO.....

Isn’t it usual to use a pyrotechnic valve to isolate the He tank? Solenoid valves present the risk of valve bounce during periods of very high vibration during the launch; the valve stem lifts off the seat. The pyrovalve provides a hermetic seal until the charge is ignited, so it ensures zero leakage during the launch phase and is only fired when that is complete.

I know that the thrusters on the mission have no previous flight heritage; I’m wondering whether other fluid-flow components in the propulsion system also lack heritage.