Understanding the Importance of Grade A Kashmir Willow Bats in Cricket: Finding the Perfect Balance of Performance and Durability
Unless you are playing at a very high level a good A grade Kasmir willow bat is your best bet. It's the best balance of durability, quality and cost. You'll only need a higher grade than that if you're playing higher level cricket. Less than that and there is a noticeable drop in performance.
The hard tennis ball in its original form might not harm the Kashmir willow bat in any way, but I guess one reason for widespread acceptance of this "fact" can be that tennis balls can get wet ( leather balls can get wet too, but generally extra care is taken to prevent leather balls from getting wet, which is not the case for tennis balls ) , and wet tennis balls might actually be harmful for Kashmir willow cricket bats. Just a guess though.