We got a very noisy apartment. The flat (as KeyHost's mostly other flats as well - see footnote) is in front of the very noisy Cromwell road. Windows are not hermetic.
In addition a strong external spotlight was located just below our window and was on all night ("it's counsil's. we can't do anything about it" they excused) and the poor curtains hardly blocked neither this strong light at night nor the uprising daylight in the morning.
For their credit it's worth while mentioning they immediately swapped us with another room (see footnote) which was a little bit better option.
In summary, unfortunately it surprised us for the bad side.

I keep saying 'they' because KeyHost is a company that runs a business of renting flats for short and long term periods.
The pros: Room is +- well equipped & maintained. They have stuff located at the building itself for any help (and I needed)
The cons: it's a company and not private asset, hence you're yet another flat out of other 20 flats or so in the building.