I actually ordered my FF/GPS combo before I ordered my yak - and that was a decision that I certainly don't regret.
I have never been fishing on my yak without the sounder, but I honestly don't know what I would do without it. It is a very good tool for finding the edge of the reef and looking for baitfish schools - as well as the larger fish you intend to target. Basically, if I haven't had any action on my bait/lure in 15 mins and the sounder is bare, I move on. I then troll a lure around until I find some reasonable echos and cast into them. It really is a time saver and I don't know how others get along without one.
I have never been fishing on my yak without the sounder, but I honestly don't know what I would do without it. It is a very good tool for finding the edge of the reef and looking for baitfish schools - as well as the larger fish you intend to target. Basically, if I haven't had any action on my bait/lure in 15 mins and the sounder is bare, I move on. I then troll a lure around until I find some reasonable echos and cast into them. It really is a time saver and I don't know how others get along without one.