They may need to be calibrated to local altitude, here in Boulder at nearly 5400' the factory set intercept was way off. The transducers measure the differences in pressure between atmospheric and submerged, our atmospheric is light compared to sea level. The dry readings have been a bit flaky however, you have to watch out for that. This is not top of the line equipment, but it may be adequate if your budget is tight, as is the project I am involved with. We have been very happy with the global raingauge we are using.
Transducers only measure depth.
The Marsh McBirney, Isco and others that were discussed on this thread measure depth AND velocity. The various pros and cons discussed in this thread were centered on the velocity measurement. They all use a pressure transducer to measure depth. ISCO also sells other depth sensors besides pressure transducers, like the bubbler. I believe that ISCO also sells a pressure transducer without the velocity probe.