I installed the pro pad mini beast 2 this spring. Although it is not a detractor if you see a deer and honk the horn they will run the opposite direction.
I have encountered deer on several rides this year going through the National Forest - where I saw deer coming out of the woods and after honking (sounds weird since it is a high pitched air horn) the horn they returned to the woods and did not enter the highway. Of course this doesn't keep the deer from running out in front of me but it Does work if I spot the deer. It also works really well in traffic. It is LOUD and has a piercing sound that gets attention of cars.
I have to say though it is not the most attractive mod I have put on my bike. It is Large and the size and the weight cause it to really shake at idle so I check it occasionally to make sure it is secure. The installation is simple.
I am Happy with it the fact that I can Really Be Heard outweighs the fact that is oversized. I try to not ride at dusk or dawn unless I have too - the HID lights I got from Jim really makes the difference at night with vision. The HID lights and the horn work well for me.