Metallothionein was investigated by multiple groups. We showed that metallothionein can localize high-copy, condensed proteins in cases in fixed cells (not cryo). 14 Ferritin (Ferritag) functions in some cases, but the 0.5 Megadalton size limits use cases. APEX and miniSOG represent non-particulate approaches to cloneable TEM contrast that result in diffuse staining and function only in fixed cells. The VIPER approach delivers exogenous iNPs to proteins of interest. It is demonstrated in fixed cells. Live cell use (required for ECT) may be complicated by cellular transfection, and stoichiometry uncertainties in labeling. (E.g., background with more iNPs than proteins of interest or incomplete representation of proteins of interest when fewer iNPs are present.) The cNP approach represents an improvement because it: (1) functions in vivo; (2) Creates stoichiometrically labeled proteins of interest; (3) Is significantly more compact than ferritin and may be engineered to be significantly smaller than the current construct.