Hello AM16,
I think the main question for me would be what your natural cycle is like. If you are a regular 28 days, then you may find that you cannot force your body into a 31 day cycle.
If you are not regular, then I feel it wouldnt make much difference. You would be taking one month less of the utro, but it might help with your organisation, however I do not know if any research has been done regarding the equivalent safety. I do know though that some women use utrogestan on a 6 week or a 3 month cycle, although they may have scans to ensure the endometrium is not getting too thick, someone on this cycle may be able to let you know.
I have always stuck with the 4 weekly as I have always had a system to know where I am in the cycle. When I was on gel sachets, I put 14 in a seperate box, then when they were used, I started the next 14, but also put 24 utrogestan in a box on my pillow so I dont forget them. I do the same now I am on patches. I put two weeks into a box, and use them then when it is the next 2 weeks I do the utrogestan as before, that way I keep track, but the same date may be easier for some people.
Hope this helps