Testing
I had a Davis Echomaster on my backstay about 15 feet above our heads on my old Mirage 27. I spoke with people with radar and they said I gave a tremendous echo return on their radar. Its cheap, light and the way I would go if I needed a new one. Maybe install 2. (see the report attached)
My current boat came with a Blipper. In the ocean, returning from Bermuda this summer, I was talking on the VHF at night with a freighter that I saw on my AIS at a range of 20 miles. We were on a collision course. He was able to see me well on radar at 12-15 miles. The conditions were fairly calm and we were under power.
Here is a test that I saw about the different detectors. The viking was recommended as coming out well in the tests. I think real world conditions are very different from the lab testing.