Production stopped: 1987 (I think)
In true Sinclair style, the machine was announced, orders were accepted, cheques cashed, and then nothing happened for a few months.
According to the marketing blurb, the QLAN connector was "a high-speed communications link for up to 64 Sinclair QL and ZX Spectrum computers." It does not, however explain why you would want to network QLs and Spectrums together.
Around the time of its demise, an adaped QL was available from another company, known as the Thor.
Another derivative of the QL was the ICL one-per-desk, comprising of a computer (still with microdrives), monitor and built-in telephone.