Without a need for money, I need to rely on this person's ability to be a professional out of the goodness of their heart. Nothing in that post or their previous work says I can rely on that. Frankly nothing in the post or their history shows they have the ability to deliver value that outweights the headache of planning, managing, and integrating them into an existing team knowing how fickle the relationship can be.
It's not similar to a contractor relationship, since there there's at least contracts and deliverables that give some clarity to planning.
There is an interesting question about whether they will contribute valuable work, knowing that they probably won't be that professional as you say. When I don't care about quality I can often produce really good results early but that might not be conventional or that maintainable. Maybe it's healthy diversity in approach for a company, better at writing interesting prototypes than a final product?
It's not similar to a contractor relationship, since there there's at least contracts and deliverables that give some clarity to planning.