Hair question: Keratin MOISTURE treatment??

Hi!

Any hairdressers out there? I recently went from dark hair to honey type of highlights, the hairdresser told me I could think about keratin moisture treatment. I did not need it though as the highlights did not cause damage.

However, now my hair is even lighter as I went back for more, in order to cancel out the yellow. He has recommended a Keratin treatment - he says not like the ones that straighten etc, but as a rehydration technique. I just can not see anything about it anywhere - only the ones for straightening and my friends have all told me not to go there. Would it really be bad? Any thoughts on this out there? Thanks xx ps this is my hair now.