The advantage of this type of airlock is that they do have a smaller chamber so you can more closely observe the CO2 rising and therefore the rate of fermentation. They are also handy when you are cooling a beer as there is less chance of sucking airlock water back into the fermentation.
The down side is that they cannot be cleaned manually if they get dirty during the ferment. That is why we do not prefer them for the active portion of the ferment when the foam from fermentation might be pushed up into the airlock.
