I'm pretty sure it's illegal to fit a gas cooker yourself, unless you are gas safe registered of course. It is a simple 2 minute job to do it yourself I agree, but what if something isn't quite right, or it's been damaged in transit maybe. I've fitted loads when I was registered, and know exactly what I'm doing, but it wouldn't be worth it as the penalties could be ginormous if you're unlucky and something goes wrong. I'm not sure if it's still the same but, when you finish a soundness test, you label the meter with your name and date on it.