An initial trial of the Xcom Global MiFi device during a pre-trip visit to Spain was not promising. The device was never able to connect to the local cellular provider's (MoviStar's) network. Even after very prompt, courteous interactions with the Xcom support folks over several days the problem remained unresolved. Xcom did, however, provide a full refund without any hassle.
Everything local with the MiFi device worked just fine. Devices recognized and connected to its WiFi network. There was full access to the MiFi's configuration settings. It simply would not connect to MoviStar's cellular data network, so there was no Internet access. The root cause of the problem seems likely to have been an improperly provisioned SIM, however, Xcom was unable to confirm that as the issue.
Not being able to pin-point the cause of the problem makes me a little hesitant about trying them again, however, the reports out there generally indicate folks have had success with the Xcom device in Spain and love the service. So, we plan to go ahead and give it another try, and bring two of the Xcom units on our field trip.
Hopefully I will have better results to report in a few weeks...