I don't think it's a good AI, in-fact I don't see much of a use for it as there are many other options to fit what ever reason you'd be using it in the first place that are far more effective.
If you're looking for a good AI both Arimidex and Letrozole will always be superior.
But the price for legit Arimidex / Letrozole is about 4x the price of Proviron...
anyway i ran Provrion twice for long periods 10-12 weeks at 50-75mg/day
but i don't think that i will run it again, im not fan of orals, unless it's 4-6weeks out and it's must,
and i think that besides the high sex drive and low price there is no reason taking it over Arimidex, Letrozole or even Masteron.