seo question -structure the links within my site for brands? example.com vs maincompany.com/example
 

i have a question, i have a site that sells several products, and for those products i have "mini-sites" within my site that explain and sell them

my question is this, i have bought the the domains for each of my product names, within my site should i have the url of the "mini-site" be the brand.com or mainsite.com/brand

which would you consider preferably and why please, your help is appreciated, thanks in advance

Without being an authorized SEO expert I would still say this:
Goolge themselves are talking about people/sites who are moving some stuff away from their main domain to be on other domains. I would see it as a specialization, and less of the be-all-approach. So If you have the domains, I would definitely put each product on each domain but maybe introduce each product on your main site under site.com/product and then a big huge link/order form direct on your big site also.

Depending on if you want to upsell one or more products to people you might still want to consider keeping it all under one domain to make it more like a store.

within your site: link to yoursite.com/brand.html - for internal linking structure
from yoursite.com/brand.html: link out to brand.com - for outbound links