The warmer keeps the nitrous from getting so cold that while your using it, it doesn't freeze parts of the system, it does nothing for bottle pressure. For bottle pressure, you want this Zex
As far as I know, the management unit in the ZEX kit doesn't help keep bottle pressure up. It just monitors the bottle pressure and adds fuel if the bottle pressure is high and takes away fuel when the bottle pressure is low. Give ZEX a call and maybe they can clarify more for you. Also, don't buy directly from ZEX, they charge more for their parts than what ZEX dealers charge.
The bottle warmer does do something for pressure. As you use the ntrous it gets colder. The pressure drops. The bottle warmer maintains bottle temperature, which keeps pressure from dropping.
The ZEX unit has no effect on bottle pressure, it does monitor it tho. And does exactly what you said as it monitors the pressure.