I have been using it for 2 years now and am 20 years old. It has kept me at a NW3 stage. You read and hear many stories about side effects from this drug and while these stories can certainly be true, what you have to realize is that side effects are common with all kinds of drugs.
Use this drug and see what happens. If you do experience side effects, consult with your prescribing Doc immediately. Think of it this way, its either take this drug and possibly slow/maintain/regrow your progression/hair or its get off this drug and become what you are destined to become, which can mean anything from staying at your current NW stage to proceeding to a full-blown NW7.
It is easier to recover from the early stages of the Norwood scale than it is from the latter. The more hair loss you experience, the more grafts and funding you will need to get an HT. In my POV, I would certainly get on this drug as most men in my family are NW6 - at that stage I would need 5000+ grafts to get a decent result from an HT (depending on several factors, such as scalp elasticity, donor density and etc.) and it would most-likely cost me $15,000-$25,000 to go through.
And also, losing hair strands is not a bad thing, it is normal. Losing thin hair strands is a bad thing as it means the hair is going through MPB and will grow back even thinner until it ceases to exist.