What my GP friend told me is that DIM can be a good supplement for women in the peri stage, when hormones are all over the place and the issue is not the significant reduction of oestrogen but the surges followed by sudden withdrawals.
She told me that some women have a natural decrease of oestrogen, leading to symptoms such as hot flushes and anxiety, but other women can go for years with huge fluctuations and she thinks this is my case and why I go from suffering from symptoms such as pins and needles, restless legs, hyperness, dizziness etc... when I'm hit by a surge and delibitating anxiety when it drops.
In my case HRT made me feel worse as I was still experiencing surges, so although it helped with the anxiety and hot flushes, it made the other symptoms worse.
DIM can supposedly help with surges as it is supposed to balance the level of oestrogen rather than give more like hrt. As said, in my case, it balanced it by reducing it, but seemed to do so too much. My friend said I should have given it longer, but I've reached the point of being tired of trying all bunch of supplements and really want my body to regulate itself at least to the point when I'll stop having urges. My mum said that she really struggled during the peri phase, but sailed through the actual menopause years. I hope it will be the same for me.
I think DIM is more commonly used in the States.