The campaign for MMP is telling voters they should vote for MMP to get a review of that system of voting.
But if a majority vote for change we will also get a review of MMP.
A second referendum will then be held allowing us to choose between MMP, with any changes to the system adopted from the review, and whichever alternative system most voters chose in the first referendum.
However, voting for MMP doesn’t guarantee you’ll get the changes you want or any changes at all.
The chances of getting consensus on improvements to the system aren’t high.
Comments from Gavin and David below points out I’m wrong on this and there will only be a review if people vote to keep MMP.
I based my post on memory of a plan to have a review of MMP regardless of the outcome of the first referendum. That obviously didn’t make it through to legislation.