Extensions can be rounded or rectangular. It's really just a preference, either of the maker or the customer. I don't like to show a button on beltless trousers, but I have seen them made both ways. Again, I think it's just a matter of preference. As for "cinching", you have two options: 1) side tabs with buckles. 2) an elastic half-belt, built into the waistband around the rear, that emerges on each side and each end buttons to your choice of two (or maybe three) buttons (on each side). If that makes sense. Neither works terrifically well, and both will cause cloth to bunch up at the sides, at and just below the waist. If you're going to get "unsuspended" trousers, best to make sure they fit, and use the do-dads for decoration.