The upsides are...Quail (COTURNIX) needs less space than chickens, scientifically speaking, they produce more pounds of eggs per pound of feed.
The downsides are: The feed is often more costly and/or harder to secure than chicken feed, and NO SPECIES OF QUAIL are the free ranging garbage disposals that chickens are. 
Now...once you know Quail (Coturnix) then 6 properly fed and lighted hens can replace a 1-2 persons egg requirements. It depends on your requirements/egg consumption, and YES, THEY ARE SMALL EGGS 
I don't know of any quail species that will lay an extra large chicken hen class egg. They are small compared to any weight class chicken, however they are prolific layers, and if properly fed/watered/lighted will produce about one egg a day until they die....Hopefully at the ripe old age of 4+ years. (YOUR RESULTS MAY VARY).
I started my labor of love about 5 years ago, with the intent of replacing grocery store eggs with my own coturnix eggs. That goal was achieved! I have since tested other models, and the results are not applicable here.
When raising any animal for any reason....There are upsides and downsides. There is no dead ringer, but IMHO coturnix fits my bill, and the bill isn't cheap by any strech of the imagination.