The modem is needed to get the best of both worlds and have a seemless local networking/wifi experience across all your devices.
It functions as both a modem (with 2 sim cards; optional 2nd card for backup data) and a wifi router for your local network.
The antenna will grab the cellular and/or public wifi network (ie: campground, rv park) signal and rebroadcast them to your modem, so you will have your own wifi network, without having to change all your devices whenever your source internet provider changes.
This antenna is a bit more robust as it will pull down public wifi networks further away than your normal router would or your devices would be able to see.
make sure you get SMA connectors as that's what the modem uses.
After doing much research I discovered this privacy oriented non-profit that has several benefits and continues to develop privacy hardware and VPNs.
You don't need to use any of that, but if you become a paid supporter: $750 first year, $500 every year after (bitcoin ok), then they will send you a 5G Sim Card that can be used in the transit max duo modem mentioned above.
It has unlimited data and is not throttled (using sprint -- now Tmobile's network). There are no deprioritization other than the standard network management that all users are subject to. In other words, most "unlimited" data plans will deprioritize you after 40gb or so.
Here is a support thread on the Pepwave forums.
I decided to get a backup simcard (my modem has slots for 2 sim cards). This is incase the Calyx service is unreliable.
T-Mobile used to have 100gb on their prepaid plan, but after calling them I could only get 100gb for $50 on a post-paid plan.
After receiving the SimCard I had to call T-Mobile to tell them to activate it since it was going in a PepWave modem. After some confusion they activated it over the phone.