Purplepenguin I know this may sound obvious, but have you checked your PS in the section on the UCAS form? If you are very close to 4000 characters and are paragraphing correctly (which you should be), it is very likely you will be over the line limit, as the lines on UCAS are shorter than the lines on microsoft word.
So you might have to cut a little bit out to make it all fit. Hopefully you can do this just by rephrasing, rather than having to cut any content.
As another person who is involved with the TSR review service, I do think it is a bit unfair to rubbish the opinions of current students. After all, they managed to write a PS which didn't make admissions tutors outright reject them! The service is guided by members with experience of admissions from the other side though, who do have some idea of what admissions tutors would like to see.
One thing I do think can be an issue with psychology personal statements is focusing on only one area of the subject (often clinical or social psychology). It is quite a broad subject, so it is a good idea to draw examples of your interest from more than one area. Psychology is also an accademic degree, so any work experience you have will be of lesser importance than your accademic interest in the subject. As a mature applicant it may have some relevance to the reason you have chosen this degree, in which case you should mention it, but focus on the reason it made you interested in psychology, not the skills you have learnt from it.
creamteas I do take your point on board, but I do think reviews have some value, especially for international applicants or those recieving very little support from school. Whilst, yes, the PS probably won't be read if the grades are good enough, I think it is good that those from non-traditional backgrounds have access to free advice somewhere on the internet which is hopefully reliable. Or who can at least tell them when something they have written makes no sense whatsoever.
I do agree that personal statements can be very formulaic, although I feel the review service does acknowledge that there is more than one way to write a PS. However, I think it is sometimes sixth-forms which push the identicit PS, insisting on applicants including a lot of irrelevant "stuff" which is probably not of that much information to admissions tutors.