I think one of the biggest problems with bowls, besides filtration, size etc. is that there not the right shape, bowls just don't work out there is not a big enough opening at the top to allow gas exchange for the amount of water people put in there. plus they just look weird, you cant view the fish very well when they are being contorted by the convex shape of the glass.
and keeping goldfish in bowls is illegal in a few country's so that should mean something.
and keeping goldfish in bowls is illegal in a few country's so that should mean something.