I heard many complaints that the tempered glass protectors pretty undesirable because many of them don't fit the 1520 perfectly because we are talking about a flat piece of glass vs the lumia's slightly curved outer edges. Around these edges the glass does not sit flush to the screen and sticks out a tad, allowing dust and things to accumulate underneath. Also, the ones that do not have this problem are because they are largely undersized and don't reach the corners, taking away from the sexy look because you have this obvious undersized layering over your beautiful gorilla glass screen that doesn't even fully cover it. So some of the image is under the glass, and some is not.
95% of the tempered glass are shipped and sold from China and because of this, product descriptions and even the images themselves are highly unreliable. Someone I know that got a glass screen for their 1520, the product image showed the glass fully covering the screen, got the product, barely 75% of the screen covered, almost like it was for another phone.
In case you were too lazy to read my life long essay, just go with a dry HD/Crystal clear non glass alternative because the glass is not a good idea because of a lot of false advertisement and bad quality.