Disclaimer: Haven't, and never plan to clean a roof.
I remember when arc's stuff first came out several years back, and I remember thinking that seemed like a good route to go for a roof guy. Obvious drawback was the lack of initial results(unless you washed the roof first).
Again, no first-hand knowledge of the roof biz....but I think if I were getting into this I'd strongly consider a push towards new homes. Preventative maintenance. Show them the numbers, how much they'll save, and then say, "hey, see that house on the hill?? That was the first house built in this subdivision, one year ago. See the black all over the roof?? Your roof will look like that by summertime. I'll be happy to come back then and bleachclean it for XXX dollars. Or, you can use a harmless product now, reapply every two years for XXX amount, and your roof will always look new."
I don't know what the costs of these services would be.....but this seems like a sound pitch to me. ESPECIALLY for condos, apts, old-age homes, etc.