Mine, after months of procrastinating, has just accepted his UiF. He did badly in his mocks and has a track record of underachieving/ overachieving ( think a D in Geog at GCSE against a prediction of B vs full marks in another GCSE) so predicting his grades is hard. he actually wanted to go to NTU but , for a range of reasons, isn't. Their offer was not a UiF, so they by no means handed them out like sweeties : NTU's UiFs seem to be mainly on their highly specialised design type courses after students have submitted portfolios.
I don't like them but it has now taken stress off. The media focus on this is - as ever- unhelpful to students. My DS now thinks his place is undeserved and that his uni is 'desperate'. He still had to make a choice between two UiFs if he wanted to go that route.
Robust research has not and cannot be done into the effect of UiFs on achievement. It's anecdotal because no one knows how likely those students were to meet their PGs, anyway . A couple of years ago , all the media attention was on how unreliable teachers' UCAS predictions are- and suddenly they are now being treated as statements of fact. My DS has been predicted BBC. This enabled him to apply to certain unis and get that offer (or lower). I don't think he was ever very likely to actually get BBC, so if he he gets - say BCC or lower - 'researchers' will say it is because of the UiF. Remain sceptical about that.
Hardly any unis have standard offers of CCC for university courses (unless we are talking about Foundation Years). DS's lowest offer was CCD , after sitting an entrance exam, reduced from an already contextual BBC. It'd be great if more unis adopted the reduced offer after proving yourself approach but I can understand many might not find that practicable. Yesterday , I found one uni in the CCC kind of ballpark for applicants and it is not on the UiF list.