It has seven sides and uses a compound curve instead of a circular arc for the side shape. The top fits securely because of the matching ridge and groove on the bottom/top. Using a 0.200mm layer height for both parts the top printed in about 8 hours and the bottom in 33.5 hours.
The bottom surface has a waffle design that saves some filament, allows for easier removal from the print bed, and helps prevent warping. Not that there is one missing row of waffle shapes. This is the result of a quirk in the design software I use (Grasshopper + Rhino) and I gave up trying to get around it.
I printed the top with no supports and the closeup shows how much better it came out compared to ArcBox8. I think the reason for this is I increased the height of this top so there was more overlap between layers.