I've had good results using my FAST unit. ( fuel/air/spark/technology) It has dual or single readers and its got a fairly decent attaching method. But, make sure you get it tightened enough so it doesn't fly off the back of the boat. I now run a safety tether attached to it.
The second time I used it and got everything adjusted I reached back loosened it up and grabbed the sensor without thinking about it. 
Sum bitch liked to burn my fingers off. Like a dumbass! I knew it was going to be hot af, but never thought about it. 
There are several out there to choose from besides the FAST. FYI: I did have a tough time mounting it on a new style exhaust. Had to come up with a gerry rigged method on that one via. a large hose clamp.