Is this better, or at least more practical than storing data in DNA?
A single nucleotide takes uses around 25 atoms from a quick count. Three of those code for 1 amino acid (the combo of three being a codon), or as a stop function, so that's 75 atoms for one function. I don't know enough about binary to know if we can engineer that same mechanism out of 1s and 0s but as another poster said, way more spatially efficient, especially if this Holmium is arranged more like a metal than an organic change.
With 25 atoms of Holmium that offers over 30 million (2^25) combinations, which covers way more than the twenty amino acids in our genetic code. So yeah even like 6 atoms could be engineered to be read like all the codons necessary for human DNA and then some.
Still all academic until you can A) put these atoms together and B) write/rewrite the information as easily as a typical harddrive. Though if that's too tecchy it could still make for an excellent one use only Store everything drive.
Also for fun just crunched the numbers, treating this as a traditional hard drive, and assuming pure Holonium, 1 gram of the stuff gives you 3.65e+21 bits. That's in the zettabit range, which is way more than I can really comprehend.