I must respectfully disagree with misterB and TSize. I love Provirin, and it's proven to be an overall steroidal potentiate, as well as supporting free test (also providing a valuable androgen boost, with zero estrogenic sides), this is fact, not fiction. Proviron has perhaps the most clinical research of any steroidal compound.
Proviron is one of the only steroidal compounds that was designed specifically for human use (IIRC, Bayer invented it in the late 1940's). It was originally designed as an estrogen reducer, so there's that.
I understand that it's not as powerful as a lot of other gear, but to me, the benefits make it well worth the $1-2/day that you will spend. I would also recommend Bayer or Schering Proviron, if possible.
Actual clinical studies have show you can run Proviron pretty much forever with no sides. I know that one clinical study revealed users had no detrimental sides after 6 months at 100mg/day, which is a high dose. I would use 50mg's/day, @ 25mg/2x/day, taken on an empty stomach (most effective on an empty stomach, according to W.Llewellyn). Doses 12 hrs apart.
It would seem Proviron would be particularly useful if you decide to use NPP. Although, if you chose to run Proviron with Tren it would/should add to the dry/cut look one would seek when using Tren. Just my 2 cents.