A few notes -- location is convenient, WiFi was wonderful, plenty of hot water for showers as well. About a 5 to 8 minute walk from the underground station.
Steps down to the apartment are a bit narrow -- not a bit deal but if you have a lot of luggage perhaps a bit of a chore.
As to getting to the apartment from the airport. If you know your way around and have modest luggage (say a mid sized checked back and one carry on per person), the underground is the cost effective option.
If you are traveling "heavy" (we were) and not keen at tracking down the precise apartment location, you can use a taxi -- we did -- two people, three checked bags, three carry on's -- set us back 80 pounds.
There is an alternative though -- set up a mini-cab -- we did that for the return to the airport -- 40 pounds with tip. You can arrange an air port pick up with a mini cab including a 'meet and greet'.
Just thought I'd share that.