I've never used Zaino (other than ZAIO), but I use plenty of sealants that I believe to be comparable..
Bis said:
So with Zaino applying very little means that while I am applying the product I may NOT SEE anything on the paint I just covered?
That's something you'll just get used to. I even apply waxes that way most of the time. On white/silver it's tough to see most any LSP unless you've used far more than is necessary.
And it will feel as if there is NOTHING being applied?
You oughta feel it going on as the product will lubricate the pad to some extent. Rubbing pant with a dry foam pad is very different from rubbing one that's depositing (a tiny bit of) product.
When doing this stuff I go 90% by feel, that and just working methodically enough to know whether I've done a given area or not.
I just have to keep "spreading" the little bit of product that is on the pad even though I can't see it or feel it on the paint, right?
It's just very tricky not seeing or feeling what you are applying. There is no way to know if you covered the area properly or not!
Again, you oughta feel *some* diff, and you'll know because you moved the applicator across an areas or you didn't

You can stop and test the applicator for product as
yakky suggested (I generally use a chrome or black plastic part instead of glass myself) or even just feel it to see if it needs more product. But I'd expect you to feel increasing friction as the applicator runs dry.
Depending on the conditions where you're working, you can fog the surface with your breath and see if that makes the product on the panel visible. FWIW, I almost always do that when buffing off my LSPs anyhow.