Roots are important yes, big time. But, for them roots, the more doesn't really have affect of needs. You still need a bloom booster regardless for of root size.
I've used a lot of different nutrients over my short growing cycle.
There really isn't 1..
Its a couple working together to bring you them perfect flowers
So an Enzyme will be key, it'll help with nutrient uptake..
As for root stim. You're coming into the stage where a lot of root stims usually get pult. So, your roots are, what they are. In the future work on your bottom in early veg and right through pre flower. Yes, biobizz and a good few others you can run through right till harvest. But, again. The time for root expansion is coming to its end. Yes, they'll keep growin but I think at this stage you need
An Enzyme, basic NPK flower nutrient, grow nute can also be used for the most part of pre flower. As its still more of a growth phase. And then a bloom booster for when you leave pre flower.
There's lots. So I'm using plagron atm. Fairly cheap.
Pure Zyme
Green Sensation
And one of their A+B grow/bloom. Certain sites have kits.
Biobizz will be your best bet from here. They've lots. Look through diaries and reviews. Are you looking to go with organic/synthetic. That'll be down to you. But, as for an all in one. Idk about that.