in your assumption that you can't watch one channel and view record another at the same time.
We have a Humax 9200T, (I think that's the model!!), which we've had for a year. It has 2 freeview tuners built in, so it can always record one and watch another.
However, becasue of the way freeview works, which is via "multiplexes", it is often possible to record 2 progas and watch a third simultaneously!
It depends on which the programmes concerned are.
Basically, if two of the programme concerned are on the same multiplex then they can both be "tuned into" simultaneously using a single tuner, leaving the other tuner still available.
I hope that makes sense!
From a user point of view the fact that there are 2 tuners is irrelevant; you don't see them. It just uses what tuners it needs to do what you ask of it. If you ask it to do something that would need a third tuner, it tells you it can't be done.
I hope that helps. Don't be put off by any apparent complication. It really is easy to use!