Any one tried one of these systems? I found one on eBay. Seems like a wonderful idea the price is a little high for my budget.
http://www.ebay.com/itm/Tru-Banks-P...rrors-HIGH-QUALITY-Teaching-Aid-/221137924334
http://www.ebay.com/itm/Tru-Banks-P...rrors-HIGH-QUALITY-Teaching-Aid-/221137924334