I bought a Sealey for about £25 a couple of years ago and it seems to work fine on the XK. Probably paid for itself when it picked up a faulty knock sensor then an EGR fault on an X Type. More recently I got an Icarsoft which is specifically for Jaguar Land Rover and gives live data etc, that was about £100 but might be cheaper now. There's lots of info on the forums about them so there's plenty for you to read if you're not into the Olympics . I had a faulty ABS sensor on the XJ and the Icarsoft picked it up no problem.
Good luck.
Pete