"Will this school truly benefit the pupils who will still have to go to the sink school?"
It's not a sink school. It's a school that was allowed to consistently underperform for many years. It takes a lot of time, effort and money to turn something like that around. The whole community are willing that to happen.
With the benefit of hindsight it's easy to reflect on what might have been if the LA had participated in the London Challenge, like other London Boroughs that have shown significant improvements in similar schools. Instead they chose to transform it into an academy, sponsored by a Swedish group with an innovative approach to education (very successful, but certainly not mainstream in their home country where they have some very small but popular schools, that people can opt into if they think that model will suit their child).
The sponsor had no record of school improvement, so the initiative was experimental to say the least. Nevertheless, the community has been very supportive on the whole, and you will find very little criticism online because people are willing the experiment to be successful.
The school's most recent open evening (the first in their striking new building) attracted huge crowds, the Head gave an inspiring speech, and many people who would never have previously considered the school were talking very positively about it in the playground over the following weeks.
I expect there will be a sharp rise in their application numbers for 2014, and they could easily be full in September. Unfortunately, their recent Ofsted report wasn't nearly as positive as people hoped, but it was still a dramatic improvement on its previous report, and with a new Head on its way there is still every reason to assume it is on an upwards trajectory.
There is certainly no reason to assume that people who liked what they saw at the open evening will automatically switch preference to a new free school in temporary accommodation, with no track record in preference to their original choice.
The fact remains that there are more than enough children in the area to fill all the existing schools and the new one, provided parents have confidence in the education they will receive. Forcing people into schools they don't like is not the answer, especially in an area where people are extremely mobile and will move house at the drop of a hat rather than risk their child's education on something they're nervous about.
There is no substitute for solid school-improvement initiatives, and the school in question will continue to benefit from intensive support until it is as good as its neighbouring schools. There is no reason why it shouldn't be.