Okay, I read the iHerb product reviews and to me they looked like one shill after another. If stinging nettle was that good, every guy on planet earth over 40 would be using it. You can try it and see if it helps you, of course, but I wouldn't do it because of those product reviews.
Also, keep in mind that stinging nettle, at best, might change your hormone levels by 20% here and there. That's not something you're probably going to feel overnight like these posters seem to claim (if at all). In fact, it usually takes men that go on HRT and double their T weeks or months to feel any difference.
Now there is one thing that might cause an immediate response with Nettle: it's antiinflammatory properties. This could potentially impact endothelial function. Furthermore, it also can reduce pain. So my suspicion is that some men have good short term results with it because of these properties and not really the androgen-altering aspects of stinging nettle.
There are a number of studies that talk about the above. Here are a couple for general interest:http://linkinghub.elsevier.com/retrieve/pii/S0014579398016226?via=sdhttp://jrsm.rsmjournals.com/content/93/6/305.short
Nettle is probably a good product, but I'm still cautious. I think most men can get to where they need to be through food and exercise and, in some cases, HRT. Of course, every case is different and some men have very advanced arteriosclerosis and various medical conditions.
Btw, I'll say it again: always talk to your doc before trying a new supplement. For example, many react with/alter medications (since they are also metabolized in the liver).