I got one of these 18 months ago:
and have been quite happy with it – it was the only dual tuner one I could find at the time, though there are plenty more about now no doubt. No need to sign up to any service, but can only record one channel at a time (though you can watch another channel or previous recording while it records). Also you can pause live TV but not go back as it doesn’t start timeshifting until you press pause.
The other problem is the recordings are done by the times given in the onscreen guide, so when the programme starts late it doesn’t pick up the change – this makes recording anything on the BBC2 quite difficult (why is BBC2 regularly running 2 mins late, does anyone know?)