It really works, try it. Check at your local flooring dealer to get the quantities, I don't remember for sure.
It is a bit messy, and make sure you let the underlayment dry thoroughly before you apply new linoleum.
If all you are doing is putting down a new linoleum, you do have the option of screwing the floor directly through the existing linoleum and not tearing it up at all, depending upon whether the existing is really glued down well, or if it is tearing up in some places. The key here is to have an absolutely smooth surface beneath the new linoleum, or every little bump or seam will telegraph through the new layer. Avoid a high-gloss linoleum and you will minimize any telegraph effects.
You can safely add one layer to the original, but I wouldn't go more than that.