You can land fish you would totally miss without it, but they are dependent on water clarity and time of day. At night, pretty useless and on a body of water like LOW you won’t see anything. In the Boundary Waters during the day, they are awesome.
As far as you get what you pay for, Vexilar’s FS800 isn’t bad but it isn’t matched to the right monitor (4:3 Camera matched with a 16:9 Screen) and its not very crisp. Marcum’s VS625SD and VS825SD are properly matched to 4:3 monitors, have 640×480 or 800×600 resolution (respectively) and come with Sony’s Super HAD III .01 Lux Cameras with 1/3″ Sensors.
Lower end models have .01 Lux cameras but 1/4″ sensors.
Like all cameras, the bigger the sensor the more light it can “see”.
There is a big difference in cameras also when considering lens type. CMOS vs CCD. CMOS are cheaper, and you can tell by the “blur” effect in some videos. CCD’s do not. So for moving while filming, CCD is usually the better choice. The Vexilar example (FS800) is a CMOS, and the Marcum Examples Are CCD’s