Epistane (2α,3α-epithio-17α-methyl-5α-androstan-17β-ol; 2α,3α-epithio-17α-methyl-5α-etioallocholan-17β-ol; 17α-methylepithiostanol; Methepitiostane; Havoc; Epi-Strong) is a product of the Designer Steroid Era, a potently hepatoxic orally active compound, but would be highly efficacious as an anti-estrogen agent, as its non-methylated counterpart (epitiostanol) is used clinically in Japan for treatment-resistant, relapsing stage IV metastatic breast cancer, as a form of alternative endocrinotherapy. In fact, it was demonstrated that epitiostanol (20mg) was more efficacious than Masteron (50mg) in treatment of male gynecomastia... its proposed mechanism is that it modulates estrogenic action at the target organ (cellular) level rather than by suppression of gonadotropin secretion.
Proviron is effective, as pickapeck says, as a mild hardening/drying compound. Some use it for libido benefits. It lowers SHBG. Some contraindications are that it (metabolism-dependent) may block Δ5 pathway of T synthesis ↑DHEA supply from [adrenal] DHEA pool for T synthesis in some individuals. It has a notable withdrawal effect upon cessation in these individuals. It is a mild anabolic, whereas epistane is potent (indeed, Epistane's Hershberger Assay results give it a remarkable anabolic/androgenic ratio of 1,100/91). Proviron is not potently hepatotoxic.
How did you arrive at the choice of these two particular compounds for your proposed use, may I ask? I am intrigued by the basic chemistry that ties the two together: their close structural relationship to 5α-DHT. So many throw around the term "DHT derivative," but these are characterized on the one hand, with Epistane, by the replacement of the 3-keto with 2,3 alpha-epithio (a sulphur atom spanning C2 and C3), versus Proviron being 1α-methyl-DHT.
Don't be led astray by their analogous features to (5α-)dihydrotestosterone, though; these compounds are remarkably different in their metabolism which is what really matters. For example, Proviron metabolizes in vivo partly to desoxymethyltestosterone (Madol), a highly dissimilar and highly potent androgen known for causing rage. Really, the grouping of these two as "DHT derivatives" highlights the pitfalls of relying on such simple classifications.