I'd recommend the apartment for those who want to stay in the heart of London since there are really no better locations in the city.
However if you'd like to rest and recharge, the (very) small size of the apartment and the terrible mattress makes you reconsider going to a hotel for a higher price.
Regarding the comfort:
There was a constant strange smell in the room, which was clean but not squeaky clean. (cracks on the wall, some blackish smudge on the ceiling in the bathroom, rusty sink, the rug might or might not been vacuumed etc.)
Also I must add the apartment is well equipped, but we had to turn off the refrigerator cause its noise was unbearable.
We got detailed instructions how to get into the house, but unfortunately I still haven't received a reply to my question whether they have an adapter or not. (they didn't had when we've been there, which is fine but it would have been better to know it beforehand).
To summarise it: you can't dream of a better apartment location wise but if you'd like to spend more than 30 minutes in the apartment apart from sleeping this might not be the best fit for you.