I think my only complaint about Malkoff products is he should have come up with a better naming convention.
M61 evolved so much over time that the early version has no relationship to the new one. Including M91T. The earlier versions had lower lumens and not running on one cell. The latest version does. M1SHO picked up twice the lumens of the early version. (nearly).Z
The Hound Dog evolved. Early versions were much weaker.
The 18650 Hound Dog should have been named something else entirely as the "Super" as these are much different lights.
So when you are looking at a used module in the for sale, you may have no idea what it is, or the previous owner may have no idea.
Maybe just move on to M62, M63.. M70.? I think the naming convention was based on Surefire P60, thus M60? Then M61. But nobody gets Surefire anymore, or their P60 modules, that's 10-15 years ago.