DM-SMR is Drive Managed-SMR. All the write/read activity is handled by the onboard electronics.
HM-SMR is Host Managed-SMR. All write/read activity is handled by specialized external hardware and software. They're far from the capabilities of most home users today.
The current 26TB WD Ultrastar and upcoming 28TB WD drives are HM-SMR. The upcoming 30TB Seagate is also HM-SMR.
https://www.reddit.com/r/DataHoarder/comments/13z7w96/lets_discuss_dmsmr_hmsmr_hasmr_and_dropbox/
https://www.reddit.com/r/DataHoarder/comments/146hb9k/information_about_cmr_to_smr_manufacturer/
Your MaxDigitalData (MDD) drive is likely CMR because they're almost surely used enterprise drives. However, be careful as there was a user whose drive was HM-SMR and unusable.
MDD is a division of GoHardDrive and IMO, are drives that GoHardDrive doesn't want to sell under their own name. Also Avolusion (externals) is a division of GoHardDrive and has been reported to contain used drives.