The pure supply with batteries initially has given me something to think about, I can now but so designate any problems. The power consumption thanks to piezo technology appears to be quite low. So no permanent Batteriewcheseln necessary. The disassemble and clean the device needs some care and sensitivity, because the device is still a little on filigree due to its compact design. A fall of about one meter on hard ground, the device will probably not survive for sure, also it is better to have as an adult in the use of children to the side if necessary. The manual is unfortunately open more questions than the declared. Thanks to the information of some reviewers here, but came to no more questions here.
So far, I can recommend the device unconditionally. If the passage of time to change that, there is again information.