oka y there is a whole section on electronics
http://www.iceshanty.com/ice_fishing/index.php?board=74.0neways ill answer your questions as short as poss and the best of my ability
First off i own a fl-18 genz pack and i know alot of people who own the fl-18 pro pack
the fl-8 does not have bottom zoom (zooms in to 1/2 " id in the bottom 6 ft of the water column) the fl-18 does and i believe the 8's dont go as deep as the 18's for example if your gonna be fishing in the 150 fow plus on the king then you may want to consider the 18
dual beam i believe is on the pro packs where u can choose a 12 degree or 18 degree transducer beam
interface rejection is a must ( I feel) im not sure if the fl-8's have them but the fl-18's do genz and pro packs simply the Gain knob on top is a button as well and u can press the knob to change the frequency u are on for instance your fishing next to someone and you are getting interference well u can press the knob so many times untill u find a diff freq that doesnt give u interfernece from the other guys vex
degree angle are how far your fish finder will read i dont know the actual formula but lets just say that a 12 degree beam at a 100 feet of water will show a 10 ft diameter of the water column on the bottom of the lake and the 18 degree may show 15 ft remember the beam from each degrre angle looks like a traingle so its skinny on top and gets wider the deeper you go so i believe the bigger beam 18 degree is better for suspended fish in deep water (100 plus)
personally i feel the bottom zoom option on the genz/pro packs are worth the extra bucks Ussually there arent many deals this time of year but maybe if your lucky u may get one cheaper on ebay sometimes they are cheaper sometimes they are more on ebay but for me i personally like to look at the item im buying at a store esp when your talking 300-400 bucks
There are enough guys in your area that will teach u how to use it bigred, robb, camo fishm, slipbob all those guys own some type of flasher
I'm no pro but I
hope this helps
FK