As good a place as any to ask: What does a bike-specific GPS do better than an automotive unit?
I use a Garmin 2460LMT in my van and on the bike, I don't rain-ride, and I don't use the sound.
Much depends on where you live. If you live in the wheat field rural areas of Kansas, you don't even need a GPS. A paper map will do. The roads are straight from what I remember when I lived there growing up, and there aren't that many people living there (@5000). Where you live, the county has about 329,000 per the latest census info. The King county area where Seattle is, has about 2.5 million people. Along with that many people, the roads become far more complicated. Not only are there more, but the number of dead ends, culdesacs, etc. makes it difficult to find a place where you aren't familiar with, impossible for me without a GPS. And the amount of traffic makes it impossible for me to spend time looking at a map or GPS to figure out where the next turn is.
So why is a motorcycle GPS important? Because you need to hear the instructions. Taking your eyes off the road to look at your Garmin 2460LMT will have you rear-ending someone in no time at all.
I used a Navigon GPS years ago to go to a BMW rally in Couer d'Alene. It had always worked fine for me till that trip. Even with a long hood, the sun washed out the screen and made it impossible to see. Being a car GPS, it had no BT sound to the helmet. I almost missed a freeway exit and did one of those last second exits across the area that you shouldn't be driving on. Later, I mistook a side street for the turn I was supposed to take and did a U-turn on a narrow street and almost dumped my bike. As I was trying to get it turned around, I thought to myself that I could easily spend more money on fixing the tuperware on the bike, than on a motorcycle GPS. Why was I being cheap? It was going to cost me more in the long run.
On that trip, the next day, it rained. The car GPS had to be put into a plastic bag. Still couldn't hear anything from it, and had to rely on looking at it for the next turn in an area I was totally unfamiliar with.
And I still remember what a woman wrote who said, "If you don't ride in the rain in Seattle, you don't ride." Not exactly true, but true enough.
Last example of when you end up wanting a motorcycle specific GPS (or smartphone that is waterproof and rugged). My post-retirement ride was to accompany a friend from Seattle to Utah to swing through the 5 national parks they have. We had reservations for each night to make sure we roomed in the same place and had a room in touristy areas. As we left, a large storm system came in and affected the first couple days. We had pouring rain for the entire first day. Sure, I could've stayed home and delayed the ride...and lost the cost of the motel rooms because I could never get down there to catch up with the reservations.
So if you stay at home in a small town community and don't go on trips, you don't need a motorcycle GPS.
Chris