I must admit I have never used the tasks and notes in the Fremantle calendar app.
As far as I understand Fremantle (calendar) tasks cannot be synced with for example google tasks (although you do mention syncevolution in your opening post). That would be a mayor drawback for me.
As reinob mentioned in the previous post, I think a lot of people would like to see an open source replacement for the current calender application.
I for instance would very much welcome portrait mode support.
But I realize that is a bigger project then your current one.