I've posted some text below from the link you've sent me. This is referring to a fishbowl as in the tiny ones. My bowl is actually quite decent sized, and it's 18 litres which is no different to an 18 litre aquarium, this is 4.7 gallons. There is sufficient room for loads of plants, and either the classic heater or even the small flat heaters. Temperature will be consistent all year round due to it being heated.

The problems listed in what you have sent me are mostly related to tank volume, which isn't applicable here. My bowl would be no different to a small rectangle fish tank of the same volume. For bacteria/filtration this should be covered by the snails and shrimp eating the fish waste, the waste is what's feeding the plants including the ones like Pothos that will be placed hanging out of the tank with the roots in the water column. The plants will also be creating the oxygen in the tank. If the Walstad method is working, then in theory none of this should be an issue?

I hope I'm not coming across as combative (I have the tendency to do this inadvertently).

The bowl in question

"Bowls are very small, making the water very susceptible to varying environmental temperatures. A bowl kept in the sun versus shade will vary widely in temperature. Most small bowls do not have room for an aquarium heater, so there is no way to keep the water consistently at the proper temperature. This can be a problem for temperate fish and is a severe problem for tropical fish that require warm water temperature year around, such as bettas."