We have a lot of small creeks in our area, and small hydro generators are common around here. The problems with them are: 1) you need a pretty big change in elevation to get enough head to turn a turbine, 2) they require quite a bit of maintenance because they get junked up with debris, and 3) they affect the stream habitat.
This floating water wheel seems to solve all of those problems.
The power output isn’t huge, but it’s constant. If you have a stream moving 4.5 mph, you’ll get roughly 4 times the power output of a 1 kW PV system that’s only active for 5 or 6 full load hours per day.