I would be using the finder mainly to find, stripers, in my local tidal river. They seem to be on the move constantly. You can hammer them in 1 spot for a few hours, and that might be it for days.
The only constant spots seem to be under bridges, and you need to find the fish to position your fly re down stream and upstream tidal flows.
My over a decade old Lowrance M68c works for the above needs. Its drawback is reading the screen in bright light. I have a portable suction cup transducer for it on yaks and prams, and we have a permanent transducer and wiring to the mount on our Jon boat. It is deadly for finding a single striper or a couple under a bridge or along the side of the river. I posted how our 11 year old grandson monitors the M68 and spots the fish and directs his Dad or I to be upstream of the flow for our casts.
The lakes I fish are water reservoirs for farm irrigation or human use. So the lake's levels and fish holdi spots change constantly from week to week. The key is finding the fish not the structure. If the big fish are chasing shad, we look for birds and the leftover shad carnage from big fish shredding and eating them. There is no need for any finder. When the big fish are gourging themselves on shad, a yak, small pontoon boat or small pram is a great tool. You position yourself upwind 50 to 60' and cast to about 10 feet from the boil and let you fly float into the boil. On the Delta, you can catch a LMB bass and then have a big striper gobble up the LMB or the reverse with a small striper and a huge LMB.
For now, I will stick with my old M68c.
Thanks again for your excellent user report and summary.
Here’s my experience using the Mark 4 DSI/GPS.
1. Excellent detail on bottom structures.
2. GPS accurate and consistent.
3. Easy to use.
4. Manual Frequency selection, to maximize performance.
5. Adjustable screen brightness.
The not so good:
1. Glare is a problem, but taping a piece of tinted anti-glare screen over the mark 4 screen helps.
2. No sensitivity adjustment (use the contrast setting, but it’s not the same.)
3. No fish arches. Fish are hard to or impossible see around the detail of structure.
4. The transponder works best in the water, it also works thru the kayak hull but there is a noticeable difference. If you use an in-hull wet mount, it degrades fish images mostly, not bottom structure detail very much.
5. Loaded Map is low quality and at times the GPS shows you being on ground. Comparing other GPS indicates the GPS in the unit is correct but the Overlay Map is not in sync.
This is a fantastic unit if you primary use is to find structures that hold fish. And you use the GPS to mark and get back to structures, it good quality at an excellent price.
If your primary use of a fish finder is to find single fish (not schools) it’s not a unit you’ll be very happy with it. The problems with the map makes this unit useless even as a basic navigation tool (Even the manual warns you not use this for navigation).
How I use the Mark 4 DSI/GPS:
On surf launches no matter how hard you try to protect it, the life of a fish finder is not for long, the less it cost the better. I use the finder to located bait schools and the detail of the M4 DSI helps me determine what bait I’m over (i.e. sardines vs. anchovy, etc.). After loading up on bait I can get out to the structures I’ve saved as waypoints without delays. Not seeing fish consistently is not a problem since I fish where there's structure, and not fish images. Most fish I target are pelagic.
Would I buy another, Yes.