by plugging in a HDD I can only record a channel if I’m watching it and not record one channel while watching another
That actually makes sense if we’re talking DVB-[C, S or T] channels received through an internal hardware tuner. A tuner can only tune in on one frequency at once. To record one channel while watching another, it would need to have two internal tuners, which isn’t very common and, I’d say, not something to expect unless specifically advertised.
Also it has developed a fault where it basically shits its self every couple of weeks and the picture pixelates. It needs to be unplugged for a week and plugged back in.
Warranty?
Don’t lay all your eggs in one basket!