Wow what a great explanation. Thank you!

I was always thinking the O2 mod deactivates the O2 sensor and gives a fixed signal. But now when I'm thinking about it. It makes sense to just alter the signal.

Yes your right. Probably the Kev mods are the best to go. I think, I will hide the Fuel mod when I drive at home (due to laws) and will just put it in the front when I'm traveling in other countries.