Do you really need the spare ball? Are you absolutely positive you don't have the ability to come up the back of the ball with speed to kill the ball? I don't care what people say, it is not that hard to do and you eliminate any feel issues switching from ball to ball (which WILL be there no matter what grip system you use). Some people have come to rely on a spare ball, but I personally feel that people that are going to miss spares are going to miss whether they have a spare ball or not. Many of the good scratch bowlers in my area don't use plastic and many pros do it just for advertising... 1 extra ball would be very nice if you can pick up your spares just as good as if you were using a strike ball.
just my opinion...
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stanski