For over 30 years I have been using premium products such as Kerastase, Aveda, salon treatments, the best tools. Redken too.
I have also occasionally tested cheap products and can honestly say that for shampoo, it's a game of roulette so both can be great, conditioner tend to be slightly better at premium, but all leave ins have been the same, they either work or they don't regardless the price.
The worst ever products I have used that left my hair looking awful were the Kerastase gloss absolu, and Elvive wonder water. I also had no luck with color WOW, Olaplex or bonding products. Sometimes a wash with headnshoulders and a supermarket conditioner have lef tit looking great, so I truly don't know anymore!
The hype and marketing is strong though.
Is there any actual science out there that can break it down? I have found some chemist related youtube's that are full of great info that cuts through the misinformation (and hype!), but they don't often answer this one.
Thought this would be a good place to ask.