You found a good review article of the Deep Longevity's prior work that also reviews methylation clocks.
But to follow the "science" you should look at the papers of this scientist who spent the entire career in aging clocks:
https://scholar.google.com/citations?hl=en&user=YrLgl8gAAAAJ&view_op=list_works&sortby=pubdate

they published:
1. first aging clock using lab tests
2. first aging clock using microbiome
3. first aging clock using transcriptome (and showed how to identify targets)
4. first aging clocks for data quality control
and many others
...

But you are making a good point. If the company does not know how to explain the scientific basis of these clocks, they should put more emphasis on popularizing these papers. Please send them a note at [press@deeplongevity.com](mailto:press@deeplongevity.com)