We have used a ShelfSpot audio unit in a temporary exhibit at the Jewish
Museum of Florida, and were very pleased with it. My office is in the gallery,
so I could hear (in the back ground) that the device was well used. There is
an obvious drawback to it: sound polution. It all depends on what else happens
in your exhibit area, how large it is, the layout, sound absorption of
exhibits or props, number of audio devices, etc. One device worked very well
for us.  There are several big plusses to the system: simplicity, compactness,
low cost, and user friendliness (one big red button is all it takes).

Remko Jansonius
Cuartor of Collections and Exhibitions
Ziff Jewish Museum of Florida
Miami Beach