Well, I ended up buying not only the Day but 10 (that's right, ten!) of the Vibe II packs as well! They were about 1/2 the price I found them anywhere else and the whole lot shipped for $5. I plan to assemble a whole bunch of small PSKs stuffed into these little lumbar packs.
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“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman