I wouldn't recommend staying at this property if you need to use broadband on a regular basis. They have a cheap 4g portable hub which was on the fritz for most of my stay. In addition, and what was far worse, was that I lost two night's sleep because the hot water system was broken (it was hot! Too hot) making a lot of noise, pipes knocking, water boiling and running all night.
After the first night, they didn't send anyone and I lost a second night's sleep. Then the handyman came and told me that the system was old and needed replacing. That there was a fault on the thermostat and he had to replace it. The water in the system was boiling with no upper limit and coming out of the taps boiling. This was dangerous but luckily I didn't get burned. The bath is large but there isn't enough water pressure for any kind of a shower. This was reported on another review and I can attest to the fact that this is indeed the case.
There are not enough blinds or black out curtains in the living room so if you're sleeping in there you are advised to bring an eye mask. I had to sleep on the sofa the second night because the noise from the boiler in the bedroom was so loud.
The flat itself was clean and adequate and well located next to Belsize village (not too far a walk to the tube but about 10-15 minutes) but overall the issues really impacted my stay. After all of the inconveniences, the most the host was willing to compensate me for was 15%, which amounted to less than two nights refund. I didn't feel this was adequate but accepted. After all that I had to manage, I didn't want to spend time arguing this point as well. This host really should consider upgrading their broadband and fixing the heating/water system. I hope the host will take on board these issues and make adjustments so that future guests have a better experience.
Guest ready (the management company) however was good at communicating and the check in and out process was smooth.