Ed....glad you got the needed info, I'm one that if it doesn't need it don't do it...and that 550 sounds like a nice unit but here in the Florida lakes that I fish it so shallow any unit is really not needed, some of the guys here who fish the St.Johns use them on a regular basis. Best of luck with the install's and on Sunday too. I'm going to my favorite lake on Tuesday it's called Orange Lake and it has some super size fish.
Mike