Welcome to the world of wood finishing...it can be confusing and even contradicting. The labels on the products in stores don't help that much. It gets more complex the deeper you go.
First, I think one needs to differentiate between stain and dye. Stain is essentially ground up pigments that sorta lay on the surface, dyes penetrate and color wood more deeply and contain little pigment.
Stains, particularly dark ones, tend to mottle on some woods...maple, cherry, pine, etc. Mottling is hard to describe, but usually looks uneven in color. Dyes color and enhance whatever is there, but in a more transparent way, if that makes any sense
Stain controller is stain base without pigments, so when applied first, it limits amount of color absorption. All this is harder to describe, but in practice is easy to see.
I should also point out that Waterlox is not poly, it's a modified varnish. Polyuretnane is a durable finish, but has a plasticky look I'm not fond of, particularly on furniture. If you want an "in the wood" rather than "on the wood" look, oils and wiping varnish will look better to most people.
If I were to suggest a system to someone new to the game, I think following the wood whisperer video would get you results you're after. I'd use Waterlox as my topcoat.
I almost hate to say it, but the wood finishing world is no different than anything else, good stuff costs more. They don't sell Wilson speakers at Best Buy and one doesn't find the best finishing material at the home centers. If you've got a Woodcraft store or something similar nearby that would be a better bet.
