FYI-FIRSTNET is NOT worth THE MONEY. Not any better then AT&T and it is ONLY for the (3) top of the line I phones out there. Their AT&T company owned stores have NO idea how to promote this. It is NOT for a Apple I phone 8 or 8 Plus. Only the (3) models above that. FYI
Have to disagree; even before I got an iPhone X S Max (had a 7+ before), I saved over $30 a month when I switched from a regular AT&T account to a subscriber-paid FirstNet account. My phone was (and is) operating through the dedicated FirstNet system core with priority instead of the ordinary consumer core. Only thing I couldn't do was operate on D Block frequencies (I can now).
So it is worth it.
I think FirstNet is good for public safety broadband data applications, and is a fine supplement to LMR systems. Viable as a mission-critical voice system, not so much; even AT&T's chairman has admitted it will probably never displace LMR. As a system administrator, the last thing I want is to have all my communications eggs in one basket.
The idea of a nationwide mission-critical system that is everything for everybody is a typical Federal "one size fits all" solution that probably won't ever be able to live up to the pie-in-the-sky promises. The problem with interoperability is and always has been training and education; you can have the biggest and best system in the world, but if the troops in the field don't use the resources available to them, they might as well be back on low band with a single channel at their disposal.
As regards the FHOF event, if I recall correctly they had the FirstNet gadgets patched through the various systems so users on FirstNet and users on MARCS or other systems could communicate with each other (without having to tote around multiple devices). That's a valuable capability.