Having a reliable internet connection while traveling is very important to us. Several years ago, I locked in a Verizon unlimited data plan with a JetPack for $65/month. It has been well worth it to us and only occasionally have we had no internet service. Most of the time we could meet all our needs, including streaming YouTubeTV. But our set up was not always trouble free, somewhat limited because the JetPack was probably not intended for the way we were using it - always on, always plugged in, internal JetPack antenna.
I knew about FMCA's plan through AT&T but didn't explore it much, not wanting to give up our grandfathered Verizon plan. But I wanted to upgrade the modem/WiFi hardware over the Jetpack. So I bought a GI-X750v2 LTE router and configured all the coach WiFi devices (13 of them) to connect to it. I then tethered the Jetpack to it via USB. It worked well and eliminated some of the random hiccups we had with the JetPack. Then I took the next step and put the Verizon SIM in the LTE router. Because Verizon is not fully compatible with the LTE router, there were problems - random and temporary loss of the internet connection. Through trial and error, I learned this problem could be eliminated by connecting the LTE router to my Wireguard VPN server at my home. I cannot explain why this works, but it does.
Loving the tinker, I decided to give the FMCA plan and after a period of testing, keep it and/or the Verizon plan. I put the AT&T SIM card in the LTE router and initially thought there was a problem. The SIM was not registering with AT&T. But I wasn't giving it enough time (free of my tinkering) to allow it to register. After a period of time (maybe an hour), it did register, and works well. Better than Verizon? I can't say. But it does seem to work well.
One of the advantages of the GI-X750v2 is that it supports multiple concurrent WAN connections - ethernet, cellular, repeater (campground WiFi), and a tethered (via USB) hotspot or iPhone/Android. I ended up with 2 connections - the internal AT&T SIM and the Verizon JetPack connected via USB. And I configured the LTE router to do 'load balancing' which uses multiple connections at once. So I am using both AT&T and Verizon at the same time and seem to be getting speeds better than either on a stand alone basis.
I'm new into this and will be doing more testing and evaluation over the coming months. I mounted the GI-X750v2 in a cabinet, out of the way. It's pretty clean and always on. In this picture you see the LTE router and the Verizon JetPack plugged into it's USB Port.