I don't know about for an individual, but for a shop they are well worth the cost. Consider that a good cleaning of, say, a Browning Auto 5, takes a couple of hours to disassemble the gun, clean it thoroughly, and reassemble. With the sonic tank, you take off the wood, dunk the gun, and hit the switch. In a couple of minutes, remove the gun, let it drain, oil/lubricate, and put the stock back on. The customer gets charged the same, the gun is just as clean (if not cleaner) and the shop makes more money.
Jim