Does the LDF LTE6 work on LTE networks in the USA?
It work even with AT&T but you must know that IMEI cannot be change at that module.
LTE6 not have all bands you can think at USA ISPs and agregation is limited by that support.
Mostly we use Cat4: EC25-AF, EC25-AFX || Cat.6: EP06-A || Cat.12: m.2<->mpcie adapter + ipex1<->ipex4 + EM12-G
About LDFR as platform, check graph of lower freq who is base at ~800Mhz and compare bands <1000Mhz who are in your ISP and you will assign some + and - to that bands, for >1000Mhz bands this is very ok base to work. I hope you can reach 100Mbps limits bcs not every Tower give us that possibility and not every customer want build a tower for lte device :).
Remember, sometimes workaround live longer then final setup 
What a great solution … ROFL