The "unpack & go" aspect of condensing dryers, avoiding the need to install a vent, is really the main advantage. They tend to be slightly less efficient and need longer drying times than an equivalent size/power vented dryer would need, and although much of the moisture from the exhaust air is condensed, they do still result in higher humidity in the room than you would get with a vented type (nowhere near as much as you would get with a vented dryer with the vent just exhausting straight into the room though).
Many of the combination washer/dryers use water as the cooling agent on the heat exchanger. If anyone is thinking about getting one of these, be aware that they can use a
lot of water during the drying cycle, which might be of concern if you're on a metered supply.
is it as easy as plugging it into an outlet and it's ready to go?
Most British dryers are rated up to about 3kW, but just watch for the slightly more powerful dryers which are available. Once you get over 3kW or so you'd need a dedicated circuit installed for the dryer.