g_man, like you I'm a relatively newbie to yak fishing. Wife and I bought 2 Ocean Scrambler II's a few years ago to see what it would be like. I'm now fully hooked on fishing from the yak and my Wife's has cobwebs on it. Would love something a little better suited to the amount of time I spend on the water but hey its working for the moment. Back on topic - I just recently bought a Lowrance Elite 4x FF, and its been quite a revelation. Unlike you I struggled to get much success on the rods other than with lots of burley and cut baits, I even bought a small setline just to keep me and the missus fed, and not damage my masculinity further by continuously coming home empty handed. Since I got the FF, I have had 1 zero day out of the last 6 trips with bait or sb. Its amazing what I had been paddling 'over' to get to my so called fishing spots, it really helped me get results quicker and more efficiently.
However - I saw the good deal on the FF and rushed into buying it without fully investigating the mounting options on the Scrambler. Long story short - a bit of drilling, cutting, sanding and lots of Selly's all clear was needed to get get the transducer installed. It was definitely not best practice digging holes in the hull but I figured I could use the FF in the next yak (or boat) I upgrade to as I'm starting to realize the limitations of the Scrambler.
I know there are guy's here with loads of experience on these matters but IMO get a FF no matter what you're fishing out of, even if its a black and white one, it will help you see so much more down there that you may not have been aware of.
By the way I live in Big Manly and usually fish out from the beach, around to Tindalls Reef and also Army bay, if you're looking for a weekend buddy.
Cheers