Pressure Regulating Valve before one tap with Instant Hot tank

Many are sold without PRV.
Some are sold with a PRV.
Do you recommend it ? Highly or partially ?

E.g. without http://www.anaheimmfg.com/products/hotwater/hot_water.html "Quick & Hot"
E.g. With it: http://waterstoneco.com/p-standard-hot-tank.cfm "Quick & Hot" and new label too

An instant hot tank is open vent, so it's unpressurized in the sense that boilover has an escape route through the teflon hose to the spout. ( Y / N ? )

The flow into it is what pushes hot water out.
Is the pressure of that flow a significant factor?
What else is there to know?

What would be its purpose? I have NEVER installed a PRV on an "InstaHot" unit, and have never seen one sold with one.

The specs for that Waterstone unit call for max 60 psi input, so I assume that they include the PRV to protect the unit in case your house pressure is higher.

The "pressure" is applied to the faucet. There is very little pressure in the tank when the water is flowing.