Hello,
TRB255 does have only one version which can be used globally.
TRB245 does not have a global version, unfortunately.
TRB2450 - For Europe, Middle East, Africa, Thailand.
TRB2541 - North America
TRB2542 - Latin America and Oceania
TRB2453 - China.
It all comes down to the modem inside and supported frequency bands. Also, different versions may have different certificates.
Regards.