I bought the Hipshot Upright Bass XTender for my classical bass to get the low Ds in a Mendelsshon concert without the hassle of detuning my E string. Easy to fit and tune, less than 20 minutes. Works quickly in orchestral setting where there is a need to quickly go from E to D tuning, and none of the noise associated with switching in an extension. It gives me almost the same range as a C extension without the high cost of the extension and the special string.