Studies on aromasin haven't shown anyone who is "unresponsive" also studies have shown that aromasin, letro, and arimidex all have very close to the same activity in males.Aromasin has a 8.9h halflife and peak E2 suppression after 12 hours, so daily or twice daily dosing is required.
Arimidex does very little to inhibit E2, and primarily works on E1.
FOr our purposes, Aromasin is better.