Although I agree that a lot of the ammonia-free stuff is marketing, I also think there are benefits.
Firstly as for it being odor-free & with less scalp irritation, I think this is a big part of our clients experience.
One thing that really surprised me when I started using INOA was how many clients said how nice it was to have a colour that didn't make their scalp itchy!
I was surprised because they never said anything when they used to have the ammonia product, either way anything that gives the client a more enjoyable experience is good in my eyes.
I don't think that ammonia is the bag guy it's always made out to be, but the majority of demi-permanent colour does use MEA rather than ammonia.
MEA wasn't used in permanent colour since it didn't give enough coverage, but when L'Oreal bought out INOA it had the same amount of MEA as Richesse.
At the end of the day going from using Majirel to INOA, there is no way I would go back to Majirel unless I had no choice. The colours look softer and the condition seems much better.
But with all the hype, there are probably some ammonia free products that are more harsh than the ammonia colours, and likewise I'm sure that there are some amazing ammonia colours out there, thats just my experience of going from one ammonia line to a non-ammonia line.