You need time on the unit to get used to how it operates (in normal operation) and how it feels when it is running normally. Once you have this experiance you can detect problems early on (such as a CO2 hit coming on). Also you need time to develop the muscle memory of where everything is.
The fact you have asked the question suggests that you aren't ready.
Enjoy your dive, which ever method you go for.
Personally since I'm a tight Yorkshire man, I'd go CCR and save the cash!
James.