I actually just tried a mayonnaise treatment and here is my personal feedback!
I used a store-bought, already prepared mayonnaise treatment that surprisingly smelled AMAZING! (It really is what they have been using at my salon for some time now .. so sneaky!) I used the Organics brand treatment and I am pretty pleased! The color is kind of a dark yellow, and it almost looks like queso chip dip LOL. I left it in my hair for 10 minutes in the steamy shower with a cap over it & then I shampooed with a 2-in-1 & conditioned. My hair is feeling VERY silky and slippery, but it is still damp so I'll have to wait a little longer to see the full effect.   

My sister once used a mayonaise treatment on her long-haired cats.   It just made them look like grease-monkeys though .  I hope it works better on your hair

I use the mayo treatment too.  It really leaves my hair very soft, silky, and shiny.  I also use the Organics kind too.

Now mind you, I have used the old-fashioned store bought mayo long years ago but I had stopped doing it that way because I didn't like the smell it left my hair.  So, I waited until the hair conditioner mayonaise came out called, "Organics."  It is really good!!