Good device, but thanks to completely outdated battery technology tuned for rapid wear. For a single or two-person household that thing like keeping two years. Four of us went, as can the battery significantly after only one year after. This thing has not even electronics that keeps the speed constant; the battery from draining or aging it, the device will be getting slower. This is technically absolutely antediluvian and is unimaginable for example in a Ekektrorasiere. The today durable Li Ion batteries (as now almost every cheap mobile phone) and a constant speed!