the meshes they sell are made for 3D app's.
there not made for 3D printing.
you would half to make them 3D printer friendly.

so ya would need zBrush or some app that has a boolean/remesher .

and since they where not made for a 3D printer .
the quality of the 3D printer friendly conversion depends on how good the 3D Artist making them is.

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The Artist that will fight for decades to conquer their media.
Even if you never know their name ,your know their Art.
Dark Sphere Mage Vengeance