Read capacity and valve labels
Capacity describes the reservoir. Valve design describes flow.
Compare milliliters with milliliters
Check the reservoir figure for the exact variant. A larger bulb is not a recommendation to use more liquid.
Look for a valve statement
A one-way or non-return valve is a listed design feature. It does not make a device sterile. Read the maker’s instructions for whether the valve detaches and how to clean it.
Check the nozzle separately
Length, diameter and flexibility describe the nozzle rather than the reservoir. Ask for dimensions when a photo is the only size reference.