Those are good non poly balls. I bought 24 off eBay for super cheap. They are good balls. They do break mildly easily. I've gone through about 6 of them in a couple months but we use them at work with people you play very rough. If your looking for the most durable ball I have ever found buy these:
Xushaofa 40+
https://www.amazon.com/dp/B00REMJM60/ref=cm_sw_r_cp_awd_NnwjxbAHQRW1E
They are Poly though.
Buy these and thank me later.
https://www.amazon.com/dp/B00REMJM60/ref=cm_sw_r_cp_awd_NnwjxbAHQRW1E