Hi Karel,
A very good document that clearly shows how different sole member and designator models are, is attached. It has been done by the ccwg counsel.
I provide a rough and non-exhaustive summary
1. sole designator lacks some of the statutory rights that sole member has : for example in amending the bylaws, the power of amendment rests ultimately in the hands of the board but in sole member it rests in the hands of the community
2. In many instances, the designator model ultimate power of enforceability rests in its ability to recall the board. In sole member, the community can ultimately take ICANN to court. [look at the reconsider/reject changes to ICANN standard bylaws in the doc.]
3. Sole designator statutory rights are weaker than sole member. for example it does not have the statutory right of inspection.
4. I am not certain but it seems like legally sole designator power in rejecting strategic plan and budget plan is limited
All in all, as I said at NCUC meeting sole membership model give us access to court. in Sole membership model enforcement mechanism is direct enforcement while in designator model it is indirect, meaning by threatening to recall the board.
Hope this helps.