Whenever I talk to people who actually do know what they are doing, I hear the same set of comments about how the logger would be vastly more efficient if we went to a custom PCB, with some specific micro controller, or that if we used a 3d printer for the housing it would look more professional. And that's all great advice if you are trying to bring something to market, but not so great if you want something that people can really tinker with.
In the spirit of Sheckley's 'Minimum Man', we wanted something with 'lowest common denominator' flexibility: so that modifications and part replacements don't require a significant re-write of the operating code or of the courses based on using them. This means that you can build your logger with whatever parts you can get your hands on, and we've now proven that loggers built with these cheap eBay modules can easily reach multi-year operation.
Our project includes a robust underwater enclosure that can be assembled with basic tools (ie: a drill, a hack saw & sandpaper) A good housing is as important as the electronics because environments that are challenging to observe, such as those underwater and underground, are still poorly monitored even though our society depends on them for vital resources such as ground water. This is especially true in the developing world where even the cheapest commercial equipment might still be out of reach: