Anyone uses the MiFi portable router with SIM Slot for Travel?

It seems to be a good solution over the "traditional" popping a local SIM into your existing phone (or to replace the existing SIM when the phone is not dual SIM), as the portable device can become a hot spot to support multiple devices with some claim up to 10!

Unfortunately when I searched it on Google, the results came back very confusing, in particular, it seems all such devices are tied to a carrier, not Unlocked.

Appreciate anyone knows something about this, posts a reply or point a direction.