See it live here: http://flatnik.com
In short: Flatnik is a good way for people to find a place to rent in London. It's at an early stage at the moment, but the main emphasis is to try things out, show it to potential users and then see if it works.
The lettings (rental) market in London is something renters are quite unhappy with. There is a huge pressure on places to live, and lettings are not only expensive but move fast. There was previously a reasonable search engine (globrix) but the #2 property portal bought it out and seems to have shut it down. Prospective tenants get charged huge non-refundable fees by lettings agencies. Many lettings agencies have a poor reputation with tenants for not managing the property, eg fixing things, answering queries. Some also have a poor reputation with landlords for being incompetent.