I thought I remembered that some time back, tournaments (perhaps just the PBA) would not allow the 4 and 6 ball side by side rollers to be used as they took up too much space in the concourse. In fact, someone once told me that is why the manufactures created the 4 ball in-line rollers.
However, being an old phart, I do not know how folks can pick up a 4 ball in-line roller and put it into the back of a vehicle. That is why I like my 4 ball roller, it comes apart easily into two 2 bag sections and I have lots of room for accessories. And, I can easily pick up each half and put it into the back of my Jeep Liberty.
But, to each his own!
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Never take a sleeping pill and a laxative on the same night.