Apparently what was broadcast on TV was only a small sample of what is supposedly a much longer cut of Tokyo Girls. So it is possible that some of what was presented on BBC Four did not have its full context fleshed out. If that is the case it is difficult to make a final verdict on this documentary without knowing whether there is more to see that might clear up bad impressions left after viewing.
Taking only this cut of Tokyo Girls into account I believe it is fair to say that some idol fans will find a lot of misrepresentation going on. There is too much focus on what might be considered the more “sleazy” or salacious aspects of the idol industry rather than being a well rounded examination. If you are a fan of Japanese idols or Japanese pop culture you may want to give this a quick look. (Assuming you can still find a copy online that hasn’t been copyright flagged and taken down.)
Just don’t expect anything new to be brought to the table in regards to the subject matter.