i dont know you personally so i cant really comment, it comes down to your skill, as i said if you are working on HE boilers and flueless fires you will be required to check CO/CO2 or CO% you need an analyser to do it, so you will decide whether to buy one depending on your workload, whether you can take it out the box, switch it on and take readings without training is down to you, check the MI to get the value you need, take a reading then decide whether the reading is under action level(therefore ok) or over action level(therefore service/repair is required) the action level info is readily available, in fact I have the FGA section from the VIPER training book as a PDF, do you want it to have a look at?