Yes, indeed.
If you need a 5 alpha reductase inhibitor, you can be prescribed Finasteride or Dutasteride, which is vastly cheaper than that product (and likely no charge to you at all). These will also effect your PSA readings, but as they are known doses, it's known how to correct for them (you double the PSA readings). If you take someone's herbal 5 alpha reductase inhibitor, no one will know how much is in it, or how much it might vary from one batch to another, so no one will be able to make much sense of your PSA test results.