I'm actually reviewing that exact shampoo on my website Hair Loss From Steroids. hairlossfromsteroids.com
I consider N2Shampoo to be VERY GOOD, but comparing N2Shampoo (or any shampoo to finasteride) is apples : orange.
DHT is created internally (whether by your balls or anabolic/androgenic steroids) and it needs to be eliminated internally as well. Ketoconazole, azelaic acid, spironolactone are all decent for topically inhibiting scalp DHT - but for the average guy sensitive to male pattern baldness - you NEED finasteride (or other 5-ar inhibitor, dutasteride).
make sure you do your homework on which steroids are best to avoid hair loss. There's a list right here that I've complied from both experience and accounting for their androgenic (hair loss/BPH) potential: Specific Steroids and Hair Loss hairlossfromsteroids.com/Specific-Steroids-and-Hair-Loss.html
Do NOT use Deca or NPP with finasteride. Note that finasteride will only help with DHT [from testosterone-ester steroids] that converts from testosterone to DHT via the 5-a reductase.