Well I've had a couple of months to practice with it and I'm generally moving in a less-wrong direction!
Today I went to a local creek. It looks like (beavers? Other rodents?) have dammed it up in a couple of spots a few dozen yards apart, creating a short stretch with a nice sandy bottom, waters with some flow but not a strong current, and a few deeper pools about 20 inches low or so. At first the water was cloudy, probably from algae and bacteria, but now it's cleared up somewhat. Perfect for a few test tips.
Dip #1 was at a shallow angle from a low bank, with the camera pointed slightly greater than about 60 degrees from the axis of the pole. I've found that some smaller fish prefer to swim between the back of the camera and the shore rather than swim in front of the lens!
Here's one of the sharper screencaps from the resulting video. Tons of Semotilus in this part of the creek!
Also saw a couple of sunfishes and some larger minnows that I'm not positive on the ID; they mostly didn't venture close to the camera, though, hanging back near the opposite bank for the most part.
After a couple of other experimental dips I wound up directly opposite from the first location, standing on a footing for the overhead pipe and orienting the camera in a more vertical position just off-axis from the pole. I call it the "down periscope" mode since it's, well, basically just a downwards-lowering periscope on a variable time delay (e.g. to get home and check the footage). It allows me to swivel around and follow a particular fish really well, but gauging depth is hit-or-miss. A lot of the time the fish I wanted was below the frame of the shot! I still got a few usable images from the resulting video, though, including one pointed a the bank directly under my feet:
Another creek chub and a surprise sunfish.
I'm really feeling that lack of viewfinder, and not being able to easily snap a photo instead of picking smeared frames out of a few minutes of video is something of a hassle. I'll have to find some deeper creeks and snorkeling gear to do better, I think.