WHAT FISHFINDER SHOULD I BUY?

I have a Matrix 25 with the GPS option and another downside is the lack of accuracy on the readout -- the default scale is pretty big -- maybe a mile per square, so it's pretty tough to accurately mark a reef, navigate a course etc. If you were driving a PB at 20 knots it would be useful, but at 3.8k, it takes a while to paddle across the screen ; )  There's probably some menu adjustment for changing this that I haven't found yet.

On the plus side, everything is right there and it's real easy to hit the big button with gloved hands and mark a waypoint.  And the screen is big enough to easily see as you are paddling. 

I agree with Mooch that if you are going to rely on the GPS for life saving navigation I would go with a seperate unit.

Here's a super cheap one:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94511

$39 at harbor freight, runs on 4 AA.  Only 100' depth capability, but that's okay for all but deep rockfish.  Should be really good for divers.

The issue really boils down to what you want the unit for.

Just depth, then go super cheap.

From there you go up in price and sensitiivty.

Want to know bottom hardness?  Want to know if the goo above the bottom is a tree or a plant.

Then you need to spend a bit more.

As a bass fisherman, and a mostly freshwater kayaker, I value high resolution and excellent sensitivity in my unit so I am able to much better to assess the areas I am fishing.

So, you really need to assess what you need from your unit to make the choice.

MolBasser