To be more specific, I'm talking about the Magellan SporTrak Pro Marine.
This is what I would call an entry-level mapping GPS. It is therefore one step up from any of the non-mapping GPS units, like the Garmin eTrex, etc. However, there are also far more sophisticated and expensive mapping units than the SporTrak as well. I found this to be an almost perfect combination of price and performance.
This is my third GPS. My first was a first-generation unit that provided very basic position plot information without WAAS (not super accurate).
My second was a marine version of the Garmin eTrex. I loved this unit because it provided WAAS accuracy, was very small, and had a database of marine nav aids pre-loaded. I did not like the fact that it was not a 'mapping' unit, and I did not like its poor reception in non-marine situations (awful reception under tree cover. It was fine on the ocean with nothing to block its line of sight).
So, the Magellan SporTrak Pro Marine is an upgrade for me from that Garmin eTrex. And, it is a big upgrade in my opinion. It is lightweight, splashproof, easy to use, reliable, feature-rich and not too expensive. It is not as small as an eTrex, but on the plus side, you get a larger screen with more data. Most importantly, it provides you with your location in the context of a map! It provides WAAS accuracy. And, it offers far superior reception off the ocean in forests and mountains.
Magellan offers a whole line of SporTrak GPS units. This one is pre-configured for marine use. What that means is that is has a database of all the water navigation landmarks around the USA already pre-programmed into its memory as waypoints.
So, as you're paddling along and pass a nun buoy marked with #7, you'll see it on the screen of your GPS already there. Nice.
It also has a basic street map of the US loaded in, so you'll see highways, rivers, towns, etc. as well.
It provides several different screens to use for navigating to waypoints, tracking your trip, breadcrumb navigation back along your route to your starting point. All excellent. The user interface is very easy to use after some practice.
My only complaint has been in trying to hook it up to a computer to pre-load points and routes and download those to the unit. It was much easier to do this with the Garmin eTrex. I suspect I'm going to have to spend some serious extra money to buy specific Magellan PC software CDs to be able to do what I want. With the Garmin, I was able to use a variety of 3rd party software (TOPO, for example)...
Overall though, the Magellan SporTrak Pro Marine is a fantastic unit for sea kayakers.