For me a big difference is the resolution.
The Oregon is 240 x 400
The GPS Map 78SC is 160 x240
More is better
I have an older version of the Oregon the Colorado and use it everytime I go out.
I couldn't even imagine putting up with the GPS Map resolution.
The higher resolution devices look like an Iphone the lower resolution devices look fuzzy in comparison but then I'm getting old.
This x 100! This was the first thing I noticed about some garmins and why I hated garmin at first. I picked up a 600$ bike one and it had the same screen resolution as the $300-400 78 series and I thought I stepped back in time! I thought I was hallucinating or something.
I was at circuit city and this salesmen walks up wearing one sequined glove and parachute pants while the stereo department is playing a-ha
"Take on me..take meeeee onnnn!"
Someone comes looking for a couple of woofers for his thunderbird, pretty in pink was on their tvs and people kept whispering about the ussr, and I just set it down and ran.
A different day I saw they had garmin oregon or Montana and a magellan explorist that have nice screens. I might be missing something though because it seems literally 90% of sailors have the gpsmaps 72,76 or 78 series which is the same as the super popular 62 series except the 78 floats and the buttons are on top. I think if I was convinced those two series were as good as everyone says I would go 62 for the buttons on bottom. I'm more used to that. But I still don't get the low res screen. What am I missing that people get these over the oregon for the same price?
To addtess Alex's point about cost. They are about the same, especially the more expensive handhelds like the oregon 650 or Montana but what I was thinking would be better about the handheld is that I could take it around the boat and sit wherever I liked using it, it wouldn't get stolen as easy because it's not fixed in the cockpit , and I could most importantly take it hiking or biking also.
Take you for example. With your oregon, you can anchor at Rosario on orcas and take it up mount constitution and track your miles and elevation. Or if you are in desolation sound, you could take it in your dinghy if you wanted to go somewhere like prideaux to squirrel cove to get supplies. unless you have a really expensive dinghy it probably doesn't have its own. A handhrld is more versatile.