I have one in my sump pit and it seems to measure the level of water just fine.

You have ultrasonic level sensors for oil tanks so I reckon that it would work in a well.

I don’t think so. I haven’t built mine yet. JSN comes with a pretty long cable, so you could but just the probe in your well and keep ESP above ground to have Wi-Fi. You could battery power the ESP32 and use deep sleep to conserve battery (you don’t need to have probe reading every second or minute, right?). You could even try to use solar power to charge the battery. Possibilities are endless.

I’m going to try to mount a probe in a sewage tank - I have a few cables left leading to it. That means I don’t have to worry about power or Wi-Fi - Esp32 i going to be at home, the probe and its control board inter sewage tank.

It is much more accurate if you use the pump. I tried just measuring the pressure in the tube from the water column, it was all over the board and the resolution sucked, probably 10X worse. Using the pump fixes that because you aren't just measuring how much the water compresses the air, you're measuring exactly what pressure it takes to push out the bottom, which is exactly the water column. It doesn't take much of a pump if all you're pressing against is a few feet of water. Something like this: https://www.aliexpress.com/item/1005009288427024.html

I'd just tie it to a heavy nut and drop it in the well. I probably wouldn't even measure it, just calibrate on some known water levels and watch it for a while.