I have been wearing the automatic/manual self inflatable vest for the last five years while wading. I wade by myself most of the time and with all the rocks and ledges in the rivers I was afraid of hitting my head also. I have fallen a couple of times, but never got the vest wet.
I don't know why the wearing of a personal flotation device (PFD) is not promoted more for safety. I have only seen two other fishermen wear a PFD. I wear the Sospender make and Stearns makes a manual one with multiple pockets for about $125.00.
I test the vest at the beginning of every year and replace the CO2 cylinder. I also carry a Simms wading staff for safety.