The bar across the top would eliminate sucking the foil down onto the central spire, but after packing a few bowls in my phunnels it wasn't hard to learn how to avoid that. Also, you can make that bar out of a small rolled piece of aluminum if it still is an issue.
The bar makes these bowls harder to clean. These bowls are deep, meaning you'll use more shisha per bowl and the shisha at the bottom won't get heated. My alien and pico use very little shisha but last more than long enough. They are relatively shallow, so less shisha will go unused. Personally I don't believe those designs can be topped.