Will this toner / colour work on my tri-colour hair?

[snoooom]

My hair is currently salt and pepper / grey at the roots, then dyed brown at the "roots" where i had a root tint, then blonde (about 2/3 from the ends upwards).
I hate the blonde, and want to go grey but I know that will take years.
I'm tempted to try this but I'm not sure how it will be on the dyed brown bits. What do people think?

bleachlondon.com/products/fade-to-grey-toner-kit

Put a bit of the colour on a section to test first 😀 easy and safe way to check if it will work before putting it on all over

I'd go to a hairdresser and get it sorted professionally.

Well yes of course. Only that will cost me a lot of money which unfortunately I don't have right now