If the binder is mostly staying inside, or not holding very valuable cards, you probably wont have much need for a zipper, but if the binder will be frequently bouncing around a backpack, or holds more valuable pieces of your collection, a zipper may be in order.
Also in Pokmon GO, new content is continually released
These cards have raised base statistics on them such as high HP, high strength and attack power at similar costs to normal evolved cards making them a tough prospect in battle
Please keep in mind that Im working with the best data possible
I like using index cards because they are sturdier than paper, are very inexpensive, and come already cut to size
The litmus test was basically that they had to have "party" in the text box or they had to be good enough to be playable in our format