I spent some time playing around with this recently and loved it at first. I also realized ChatGPT is pretty good at generating Mermaid diagrams (didn't try your own AI features).
However after getting into it some I ran into some significant frustrations. After creating a medium-complexity diagram, I was excited to see the Whiteboard feature to drag things around / improve the layout manually. But it really started breaking, it just wouldn't let me organize/drag things where I wanted, and I couldn't get things to not overlap. I also wished more diagram types supported Whiteboard (I noticed some didn't).
Also I some confusion between the capabilities of mermaidchart.com and mermaid.live. Are these competitors? Variations of similar apps. I was confused. Also "Playground" vs "Live Editor" is confusing.
Overall glad this exists and hope it continues to improve.