I got the 30FF through Amazon after purchasing and returning a 30F from another retailer. I am usually a UK 30F or US 32DDD, but I do have a few bras in 30FF, without the difference from a 30F being as significant as with this bra. The 30F was ridiculously small. Band was super tight, which I could put up with, but the cups were extremely shallow and small. Major squishing and spillage. So I wasn't sure going up just one cup size would be enough. It seemed I would need a 32FF (up one band and up 2 cups all proportions considered), a size unknown to me so far. But after carefully reading reviews, I saw that many customers who had found the bra very small got satisfaction by going up just one cup size, so I took that chance. Good call: band fits very nice (even though it's still a 30, what gives?) and cup is ok.
However, it doesn't give the nice rounded balcony shape I see in most photos. It doesn't lift tissue up from the bottom despite the seams. This is because even though wider, the FF cups are still somewhat shallow. So while it supports and fits, it doesn't provide the best of shapes. However, if I bring the straps closer (as if I was going to crisscross them), then there is some rounded lift. It is said that the straps only provide 20% of the lift, but in some bras, I think they do more. In this case, they are too thin for a 30FF to do the job (and not fully adjustable). So I might replace them.