This is for measuring respiration in small chambers where we want to minimize contamination of water oxygen from air, hence the desire for a small probe that can enter the chamber.
May want to consider the OxyLite here. The system has a variety of small sensors and responds almost immediately to changes in O2. the main reasons I would suggest this system over others is there is no calibration needing to be done on sensors and these sensors do not use oxygen to take their readings which can clearly be an issue in low oxygen environments.