Notion can be used with Studio One and should be the missing notation part ot the DAW, but in this state its not very handy. You must save a track as midifile and import it in Notion, then you have to enter the rewire-mode to let them play together. Thats no good workflow. There should be a direct connection between these both programs like it is with Melodyne. Notion should be usable as Vst. You should be able to mark a midi-event-part and then - with right-click- open it in Notion. Then Notion and SO1should play together without rewire.
Look at a program called RapidComposer, in which the Vst-function is realized.