Anyone have an opinion on mobile hotspot by CalxyOS?

Hotspots work well. They are hotspots though, so you have trade offs. For instance, you probably don't want to leave it on all day (because it won't last all day, probably 8 hours). You can set it to turn off if there's no connected devices for x minutes to save battery. When you turn it on you need to wait for it to actually turn on and connect, then have your phone connect. It takes a while, relatively speaking (not long but longer than turning on your phone).

The Mifi X Pro also has an Ethernet port which is convenient for hard wiring a laptop.

The service is solid. Overall there's no issues. I've had issues in hotels, but it's a T-Mobile network so I'd presume a standard sim card would equally have issues.

Privacy is an interesting take. I'll go ahead and trust them to not share my data (which you can sign up anonymously if you wish). The number is still trackable though, and I'd suspect stands out more because it's in a specific spectrum range. But the sim isn't in your phone, so it's not technically tracking your phone (and a side benefit is you can't get sim jacked) and I use a VPN to connect to it as well. I don't think the sim card tracks the same way because there's no GPS in the hotspot, but of course it still calls out to cell towers. I don't know if it does this when off like a phone does (I've always presumed it does).

Overall my experience has been a positive one. Choosing a phone service has been a harder issue for me. But that's another story.