Just did some testing,

you can link even the same ad provider on multiple firms and have it run additional budget additively per product, and even for the same product.

This is just like having one free ad unit per product/per firm with the same functionality (brand is local as it was always)

Thing is, you have to remember where you are doing advertising as usual... It would be helpful if there was a seperate info tab for that, to chech firm spending on advertising...

From the cap2 manual and from what I know of the game,

page 33
"Setting the bar (click and hold the left mouse
button and drag the red slider to set the value) all the way to the right will
saturate the city with advertising. This may have a negative effect on brand
loyalty if you cannot satisfy the increase in demand."

So whats the range of the built in advertisment unit? does it do worldwide ads? Or is it just based on the selected station, and works like it used to, with the idea that it's just sitting on a virtual unit?
(as to have to set the ad budget per city per product)

Does this mean that if i sell the same product in multiple stores, the hidden ad unit will be identical? i.e. one per product per city? Or does each store have one hidden ad unit per product, and thus I can set more than 1 up for the same product?

Also does this change how brand awarenes gets around at all?