Hair stylist chiming in!
MEA and DDP is in every conventional haircolor.  There are some off brands that do not include these chemicals.  As stylist we need true, consistant results.  "Organic" hair color may work beautifully for some, but in a salon, where we apply hundreds of applications in a year, we must use predictable color.
Henna is the only true organic color.  Those of you that have used it frequently, and I'm not talking once or twice, can attest that the results vary greatly.
MEA is a non volitive ammonia.  Is it better?  Well, it is not swelling your cuticle open the same degree that traditional ammonia.  It has been used for DECADES in demi permanent color and in almost all "organic" permanent colors.  That's right.  Every recognizable brand contains MEA.
DDP, it is the second bad boy of color.  This is pigment in color and usually the reason behind allergic reactions.  It too is in virtually every tube of color.
I am shocked that with the hype of ammonia versus MEA, and DDP, why people do not stress about the latex gloves that most salons use.  It is far more common of an allergic reaction.
What it boils down to is find a stylist that you love that listens to you.  Trust that they stake their talent and the reputation into the color they use.  They have put more time than you can ever imagine selecting the best color for the effects of the climate you live in.
Side note...we switched from the most popular "organic" color to INOA and could not be happier.