I have one and have had it out for the first time this season. I am using them with my cage traps, and so far only one non-target catch. A great horned owl. Opened up the door, and he didn't hesitate taking off out of there.
In my personal opinion, you need to find a location where you can place the device far enough back in the brush, and then create a couple of avenues to the device and place your traps there. With no volume control, it is very loud, and I believe too loud to have a predator come in close range for a trap.
The one I have in the field right now, I have had grey fox come up within a few feet on two different occasions, without committing to where I have the trap close by. I need to re-make the set and create more distance between it and the trap. Best of luck to you.