Modems in Mexico

We are getting ready to order 50 notecards for a Mexico evaluation. Which would be the best unit out of the LTE Cat-1, Cat-M or NB-Iot Global modems you offer and if it’s a toss up, which one will use the least data?

Also, I am intrigued by the statement on the page:

Alternatively, host your own Device service based on our open source reference implementation.

Can someone elaborate?