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The leather pouches are NICE, I agree, but some of them will have the chalk occasionally bounce out. Also, the pouch gets dirty with repeated use.
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That's right, Joey. The poolrooms I frequent have pool chairs with arm rests (with scalloping along the outside edge of the arm rest, to rest your cue). Sometimes, when sitting in these chairs, the leather pouch would "catch" on the inside edge of the arm rest, bend away from my body, and then release like a catapult -- flinging the chalk on the floor to one side of me.
With the rare earth magnet, the chalk cube may catch, but it rocks away from the magnet and then snaps back. Never had a problem with something "removing" the cube from the magnet -- it takes a hand with a grip on two sides of the cube (or "lip" of the metal disc underneath) to remove it from the magnet.
-Sean