The retail shelf is where a customer first encounters the barcode and other aspects of the product label (like nutritional information and any standard label included on it like "kosher" or "dolphin free").
Because a customer moves past many such shelves rapidly, this is probably the worst possible point to ask them to use a worn device, certainly not one that they must pull off a belt or out of a pocket to use, or which is not handsfree. For these reasons the headset is the best device for delivering any detailed information at this location.
This and the checkout counter are the only two guaranteed places in-store that the customer will encounter, so any Consumerium Service access should be optimized for these. In friendly retail locations, e.g. the Big Carrot type store or local co-ops, it might be possible to augment the shelf itself, if the institutional buying criteria of that store are likely to closely match the individual buying criteria of the customer. In that case, the Consumerium buying signal's positive choice information becomes a definite price premium factor, and the whole store will probably be able to charge more for providing such complete profiles of what the customer is buying.