The DK’Tronics Keyboard & Case was an after-market upgrade kit for the ZX Spectrum. For £45 in 1983, which is £160 ($210) in 2020, you would receive a keyboard in a new case/enclosure. You would then strip down your original ZX Spectrum computer and PSU, and fit them into the new DK’Tronics case. This would give you an easy-to-use keyboard with full functionality, as opposed to the Spectrums original rubbey keyboard which was almost impossible to use.
DK’Tronics were based in Great Yarmouth and ran from 1981 until 1994. Their ZX Spectrum keyboard was regarded as the best on the market.
World of Spectrum has a very good website on DK’Tronics, including hundreds of adverts for the keyboard upgrade.