Great for brainstorming, but simply awesome for the next stage, when the sitemap needs to be more formalized. You'll get enough structure to have control and overview, while still being free enough to move things around and do things "your way". Really easy to use, not overwhelming like other tools can be.
The free plan can feel a bit limited, but enough to get started. The pro plan is great, but the price step up to the team plan is a bit steep when you're a small team (1-3 people), I must say.
Tweek