Asus is not done with the Zenfone 3 Max series. If the 5.2-inch model with the MediaTek processor wasn’t your ideal match, then perhaps this new, larger 5.5-inch model will be more to your liking.
The most noticeable differences other than the size, is that the ZC553KL comes with a 1920 x 1080 display which is more than the 1280 x 720 resolution of the ZC520TL and the processor which is a Snapdragon 430 compared to a MediaTek in the smaller Zenfone 3 Max model. Camera specs are slightly better on the ZC553KL as well. Pokemon Go fans, be aware that the ZC553KL comes with a Gyroscope whereas the ZC520TL does not.
It’s going to be interesting to see how the higher resolution display might affect the battery life between the two phones. The Snapdragon processor in theory should be more power efficient, but we will hopefully find out soon how this new ZC553KL model holds up.