Thanks for these comments, especially with your firsthand experience. I don't disagree with anything you are saying. I've been running into this conversation a lot now with GO! in which someone would like to use the GO! strictly for emergency calling which I wouldn't necessarily recommend because it requires a secondary device and you can't just pick it up and make a phone call like you can with a handheld.
I will, however, just interject on the GO!'s ruggedness in that it actually is a very rugged device and is rated the same as the Iridium 9575, but your overall ruggedness is ultimately dependent on how rugged your smartphone is since it is required for a majority of the functions on the GO! outside of tracking and SOS (and I think this is what you are alluding to). In some ways, I would argue that the GO! is actually more rugged because of its form factor and antenna design, but I think that gets into splitting hairs.
Believe it or not, there are a lot of people out there using Iridium handhelds for data, and the primary reason is that it is the connection they have available and would otherwise not be able to do anything. In the case of using Iridium for data, the GO! eliminates the need for the axcesspoint if you are wanting to only operate off of a smartphone or tablet, and thus eliminates one component (assuming you are already carrying your smartphone/tablet)--and it comes in at an overall lower price point.