The combination washer-dryer units are often condensing dryers, as both a cold water supply and drain outlet are already available on the unit for the wash functions (obviously).
For anyone not familiar with the principle involved, the condensing dryer works by directing the hot, moist exhaust from the drum over a finned condenser which is kept cold by pumping water through it. The cooling effect on the air causes the moisture to condense so it can be collected and drained away along with the water supply.
Personally, I would always go with a conventional vented dryer if it all possible. They tend to be much more efficient, and don't use water either (important to consider if you're on a metered supply).
With regard to the electrical hookups, dryers up to 3kW can be plugged into a regular outlet here, but be careful of putting too much load on one circuit. If you connect a 3kW dryer to the same circuit as your washer, dishwasher, electric kettle, and other large appliances then try to run everything simultaneously, you risk blowing a fuse or tripping a circuit breaker.
If you opt for a more powerful dryer (over 3kW) then it will need its own dedicated circuit, as in the U.S.
