The one difference the literature points to is a block and tackle balance system on the Elite whereas the Mezzo has a coil balance system.

Same window. They change the balance system and there may be another minor change to justify the name, but essentially it is the same window with the same pros and cons. It is an improvement over the old model, but far from the holy grail of window choices which would be a product of tremendous quality and performance at an insanely low price. Still much, much closer to the latter than the former IMO.... Also known as a Gentek model, and window world.

From what I've heard and read (which is not much) still a mid-grade window ?

I think that is a fair assessment.

The numbers on it are improved, but I have inspected and operated a unit and "mid-grade" is pretty generous in my opinion. It is one of the lower priced products on the market, and the quality seems to be right in line with that.