So far so good with the topical fin. It may be a coincidence, but since starting fin my erections have definitely been firmer. Increased libido too. I should probably knock on wood when I say that, because its only been a month and the wheels could come off anytime. I debated whether to go oral or topical. The advantage of the oral is the fact that all the hair on the top of your scalp (and your donor to) can benefit from the reduction in dht - simply swallow a pill. That would be advantagous for me because I have some diffuse thinning. The downside, of course, is the greater reduction in systemic dht and increased risk of side effects which is what ultimately led me to go topical.
As far as the topical goes, the more hair you have the harder it is to actually get it applied and rubbed into your scalp. Pretty easy to miss spots. Just for kicks, I had buzzed down to a #0 at the same time I started the fin. Application was a breeeze at the point, as I was essentially rubbing it into a bald scalp. Now, a month or so later, I'm having to get through a bunch of bristly 3/4 inch hair which isn't fun.