Here are the LTE bands for AT&T:
https://en.wikipedia.org/wiki/AT&T_Mobility#Radio_frequency_summary
700 MHz Lower B/C/D/E 12/17/29
LTE 4G Bands 12 and 17 are the main LTE bands for coverage. Band 29 is only for supplemental downlink.
850 MHz CLR 5 Active & Being deployed as needed Additional LTE bands for capacity
1700/2100 MHz AWS 4
1900 MHz PCS 2
2300 MHz WCS 30
Also
the device has to be unlocked, but these are the bands the M1 supports:
• Max 1 Gbps download speeds, and 150 Mbps upload speeds
• LTE CAT 16, 4-band CA and 4x4 MIMO
• Up to 4X Carrier Aggregation
• LTE/4GX 700/900/1800/2100/2600 MHz
• 3G 850/900/1900/2100 MHz
Here's what the Unite Explore supports:
LTE Bands: 2, 4, 5, 12, 17, 29, 30
4G/3G: HSPA+ 850/1900/2100MHz - Global roaming supported.
So pretty similar to each other but the explore doesn't have the 4x aggregation.