I started in GPS with a Garmin GPS III and a Lowrance GlobalMap 3000MT. I liked the GM's display size and user interface, but not their total lack of support or care about maps that they didn't already offer. The Garmin "GPS x" family is perfect for how I mostly use a GPS, just a little small in display size though it does have remarkably good resolution. I currently have a GPS V that I will use until it dies, which will hopefully be a very long time as it's potential replacement (276 or 376 series) isn't particularly inexpensive.
I was given
Overland Navigator for Christmas. I'm currently loading it on my Asus Eee netbook, which has a 10" diagonal screen and is 10.5" wide in total. I intend for this to be my new, large display GPS system. (I also use the Eee as the digi-pics repository, larger screen digi-pic viewing, emergency race radio re-programming, and for net access while on the road.) The O.N. program needs a GPS reciever, but the 'hockey puck' that Spacial Minds offers is nothing more than a magnetic based dongle on the end of a semi-long USB cable. Could probably also use one of the
Gilsson GPS antennas, but I've not verified that. So two cables (power & 'antenna') comprise the total cable mess this system needs to function. One more than the GPS V needs, but the same as the Lowrance.
I tried a Lowrance Baja HD5 and well like you mentioned their complete lack of support and/or map source pretty much makes the unit useless (to me) and my chief navigator (my wife), so down the road it went. I found my Nuvi (couple of years old) was easier and at times more accurate than the Baja. I tried Overland Navigator on a laptop, loved the interface and maps, but the big glaring issue I found was that it is set up as a "North up" only configuration, which made it very difficult after many years of using track up to figure out what I was looking at (maybe I'm not that smart...)
So I am back to my Nuvi with my topos loaded.
Someday the perfect vehicle based GPS might come out, but I don't really expect it to. Something like the Montana with a 5 to 7" screen would be the bomb. I love the fact that when I hit the pavement, I switch map sources and the nuvi works for the road, when offroad, I switch to the topo map and I'm good to go. My problem is that my nuvi is too old to show much detail on topo settings. That's why I have an Oregon when on foot.
Jack