Injection molding provides a number of advantages over most additive fabrication techniques, such as 3D extrusion printers. Even with small, manually operated appliances, the parts produced on an injection mold machine will have a better finish and greater strength than those produced by a filament extrusion 3D printer. Also, injection mold machines can typically support a wider variety of materials, such as various rubbers.
Of course the real advantage of injection mold processes is speed. Once a mold is created, a part can be finished in minutes, if not seconds. Consider a button. These can be produced in seconds on even a manually operated injection mold machine. On a 3D printer, you should expect 15-30 minutes; sometimes longer. Printing six 1cm x 1cm x 1cm calibration cubes (at once) on our various printers takes anywhere from 2-3 hours.
Getting the speed advantage of an injection mold machine, however, requires an up front investment in designing, testing, and then finalizing a mold for the desired part. This is not trivial.
For our weather station project, we do not foresee any country placing more than a hundred stations, and we would claim victory after a couple dozen fabricated, calibrated, fielded, and operating stations. In our envisioned application, slow production of stations is okay, if not desirable. The intent is not to deploy 100 stations at once, but rather to do so over months and even perhaps a couple years. This has several advantages, but the most important benefit is not outstripping the absorptive capacity of a national weather service to place and maintain equipment. Another advantage is an ability to slightly iterate and customize parts, as units are deployed, thereby integrating lessons learned in the middle of a project.
Having weighed options, an injection mold machine in the MMA project would likely only be used for highly detailed parts, or those that require special material. Otherwise, the investment in a high quality mold outweighs the benefit.