I'll add that the FL-12 & are are basically the same.Different look to the screen. Both FL-18 & 20 have the zooms.The 20 also has a day/night setting and external power posts.I never have found a use for the zoom.I've learned how to read my 8 & I keep the gain down so I see the eyes flickering in on the bottom.
Technology advances are, at the least, amazing! After reading these posts, I broke out laughing and I mean really hard. I started thinking about MY depth finder, an old Shakespear purchased in the late 1970's. The unit is handing from my garage rafter (probably with a severely corroded battery) and the transducer is somewhere on the bottom of Lake Big Sissabagama in WI. I never thought my 6 HP Merc. would have enough torque to rip the suction cup mounted transducer off, but it did.
One of those "Well, I'll be go to he**" moments!
I guess I am going to have to visit some of the mid-winter fishing/boat shows we have here to get up to speed.