The key points are that TXL is very close to the centre and taxis are cheap. The airport is set up so you don't need to spend much time there (therefore there's not much to do). The check in is in front of your gate and you can be dropped off right outside the correct check-in area for your airline, this does mean that the check in desks are tied to the flight that is departing from that gate at the time.
If you're familiar with how it works TXL is a great airport as it minimises the time you need to spend there and is conveniently located.