chitown...
The Slate Blue might be discontinued...but the replacement is already in the works according to Jason at Visionary. The thinking is that it will be a harder (than the S.B.G.) urethane cover with the Ogre core.
But about the urethane "need" or "lack of need" -- it's all relative. If you don't run into a condition that requires it, don't buy it. If you do, and you are positive that nothing else could work better, buy it. There is no reason for this huge debate. The fact of the matter is that a urethane ball with a decent core WILL give you a unique look not entirely able to be replicated by a reactive (no particle or particle) ball. You might come close, but it won't be the same.
I personally believe that there are conditions still out there that you can use a urethane ball on. On Saturdays, the closest bowling alley to me presently (in Charlottesville, VA) puts out the weirdest shot imaginable, so the kids with no hand and plastic balls can hook it 5-10 boards. After I coach the youth league, I try to get in a few games, most of the time using my White Dot, since everything else I have hooks too much. The shot is really short -- maybe 30 feet -- and the lanes are old, beat-up wood. I honestly think they put the oil down in strips. I might as well be bowling in the heyday of plastic and urethane. In any case, when the oil is still fresh, I might be able to play outside of 5. If not, you have to move in a bit, and send the ball away. Often, though, what happens is that the White Dot just can't corner because of the cover and the pancake core. Reactive resin covers literally take off half way down the lane. The only time they don't hook too much is when you purposefully make them roll out. A urethane might give me some early roll (hold), but then not make that huge change in direction until later (if at all). Perhaps one could play a fall-back shot, which normally cannot be done with the polyester ball since it hooks just a few boards too little. For those of you wondering, though, I have not tried a Clear Diamond or XXXL. I figure that those two are another option, however.
Just my thoughts.
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I am the University of Virginia's Bowling Team. After all, one All-American is all you need.