Less clutter. More focus. Especially on the kanban board page. This will be completely focused in on your project and tasks only. Think of a clean modern writing app these days with hardly any GUI. It lets you focus on writing. Now apply the same sort of style and feature to a kanban board. Very nice to look at, awesome, addictive functionality within the board which motivates you to get your project tasks or tickets done so you can interact with the board.
Intuitive task list view which will let you efficiently and effectively see your workload in a slick, productive list - Again, gives you that ability to really focus in on what's going on.
There will be some project specific settings in terms of if it's a personal or team project which will be highly beneficial.
I know trello has customisations in there as well but Simple Board will provide this in a configuration / settings page which you control completely from here, again, separating this cluttering functionality from the actual board itself, allowing you to really focus in.
A lot more I could say at this stage and a lot more that will most likely be added as I develop.
My idea with the term "addictive" is that the functionality of the board and overall experience leaves you wanting to come back for more. Thus empowering you to complete project tasks and items on time / increase your productivity. Which in reality is what a productivity tool is all about.