GB_Amateur,
Yes, the Garmin model with the InReach is the Garmin InReach Explorer+ you linked to at amazon.
I have a Delorme InReach Explorer, the Delorme model you linked to as well.
I use a Garmin GPSmap 62s for navigation, and the Delorme, for emergency response and simple texting like (All OK, headed back) as preset messages since it is such a pain to manually text using the Delorme. I imagine if I had the Explorer+, I would only need to carry one unit instead of two, as the Delorme Explorer is more for emergency response and communication than it is for navigation.
Depending on whether or not your situation requires the InReach communication, the advantage of paying the extra $160 is that you wouldn't have to pay the $289 just for the explorer, and then buy a GPS for navigation. All of the Delorme InReach have monthly/yearly subscription plans just like a cell phone provider. I think they vary from $5 a month to $35 month.
My explorer usually sits in the glove compartment of my truck, with its cigarette lighter charger waiting to save the day.