I think this could be difficult. You can see certain patterns or fish, but the drone will not float in the water, but lie on the bottom, which will only give a small wave, if any, in the sonar. You must not imagine this as a 3D image of the ground, but only a 2D map as you can see in the product images / videos. It will be difficult to recognise a drone here. You will be more successful if you grab a pair of diving goggles and go splashing around on the off chance. If you want a sonar for fishing anyway, this is a nice gag and also shows some info. But for drone fishing only, I wouldn't recommend buying it.

I think not. I also have a real sonar but I think the interpretation is very difficult and needs a lot of experience. A "real" sonar is soon 700-1000. I'm not a professional but I'd rather spend the money on a new drone. Or find a professional with sonar. Or a diver.