I have had mixed-experience with Sprint. The Franklin R910 is a piece of garbage in my opinion. We use our RV about 3 months out of the year, we live in Northern California, so we do not necessarily have to escape the weather, it's just for a change of scenery. We are also in a rural area, and California is probably the worst for rural Internet service in the US. We do have a "barely functional" DSL, with speeds that have not improved since we bought our house 25 years ago.
After receiving the R910 from FMCA, I thought I would be a little creative and put the Sprint SIM in a MOFI-4500 I had from a brief trial of service from UbiFi.com. UbiFi was good, just quite expensive (about $90 / month) and they only offer AT&T - which was very slow in our home base area, if you are interested, it is here - https://www.ubifi.net and would be pretty much universal service, just slowish at about 10 mbps. I do have Internet service at the house when we are here, it's also not very good and I'll usually work in my home office using whatever cellular device I have. The DSL is basically just for the home automation stuff, and the TVs work somewhat reasonably well on it (one at a time).
Anyway, for about 6 months during our winter "home" span of the year, the MOFI 4500 worked fabulously with the Sprint SIM in it, literally, it never went off - never a reboot, dropped connection, etc. I do have an external antenna for it mounted on the roof of the house, and another one on the RV. When using either, I just plug it into the coax going to the roof and it always has perfect service/coverage. The MOFI is not as fast as the Franklin device, it's a little older and doesn't aggregate antennas like the Franklin does, but it is also commercial-grade and very reliable. The MOFI also works with any carrier / any technology.
About a week ago, Sprint seems to have noticed, and the MOFI will only stay connected for about a minute before losing service. Nothing I did would work to get around it, the logs just show it being booted from the network. I put the SIM back in the R910 and it works fine. Unfortunately.. we went from about 60 mbps of service from the Sprint/MOFI solution to back to around 6 on landline DSL (for the house). I still run my business and I teach MBA / graduate classes for a major univeristy via video conferencing, so that's an issue... I'll probably end up doing a satellite service for the house or some other weird solution. The limited data plans on the others would get eaten up pretty quickly with all the video conferencing that I do.
The R910 experience is truly awful - it seems to overheat at about 12-14 hours if I leave it on, (which then breaks the alarm and automation on the RV), I popped the battery out of it thinking it would avoid an overheat, but works even less then - only staying on for about 20 minutes before rebooting. The total hours of usage on the R910 that I have shows about 30.. so it's not like it is "worn out" by any means.
The Sprint service itself is fairly decent - when in range of a tower, I hit 70-80 mbps with the device, which is actually slower than my iPad Pro with it's Sprint service - I routinely reach over 150 mbps with that (on cellular!). Coverage in the Nevada Great Basin (which we travel across frequently to escape California's communist leanings) has been very spotty on Sprint - many places we stop, we get zero service, on our Sprint phones or the hotspot. When it works, it's great, but there are a lot of "off" places.
Verizon coverage is generally better, but I think the network is a little slower. AT&T does seem to have the best coverage, but it is very slow.. I originally had an AT&T SIM in the MOFI from Unlimitedville and I never got above 8 mpbs.. it wasn't worth the enormous cost increase versus the regular old telephone company DSL for the house, but it did seem to work pretty much anywhere.
My two cents - I would recommend FMCA offer an upgrade-plan with better hardware like Unlimitedville or UbiFi does - offer both the easy-to-use little made-in-China Franklin things, but also the Sierra Wireless MOFI 4500 devices or similar for an extra setup cost, although they are a little complex to use - just ship them pre-configured. People will be MUCH happier with them. "Unlimited service" really isn't unlimited if the thing crashes every 6-8 hours.