When you are looking for a banner material surely the weight of the material is a clear and easy guide to what is the best quality? 510 grams is more than 440 so it must be better. Unfortunately, the market is no longer that simple and weight can be a red herring when it comes to run ability, durability and machine and ink compatibility.
The coating of a banner material is there to give you an attractive look and feel, but it is also there to hide what is inside, or what isn’t. To understand what you are buying and if it will be suitable for the task at hand you have to understand what lies beneath the coating. Much like people, or a jam sandwich, the important stuff is on the inside.