It's minimal but at the cost of cutting some important features.
Can't add notes, Can't create multiple topic within one board, No grouping, No custom colours, No connection between two topics or subtopic with arrows

Apart from that, It's really easy

Suggestions:
- Custom Colours for topic/subtopics
- Notes
- Arrows to pinpoint different topics (Miro has it!)
- Select multiple subtopics and assign them a label (to group)