It will be interesting to see if the drug catches on. Viagra is such a well established brand, it's synonymous with erectile dysfunction drugs as a class (that may actually be a synedoche, rather than a synonym, but I'm not sure - it's been a while since Lit 101). Viagra has a loyal following, especially among older users. Not to stereotype, but with age sometimes comes a resistance to change - or an attitude of "If it ain't broke, don't fix it."
So unless guys are really unhappy with Viagra's wait time or having bad side effects, I would guess that not a lot of current users would switch. On the other hand, Stendra might appeal to younger users looking into using ED medication for the first time.
The 30 to 60-minute lead time required for Viagra works adequately for couples who have an established sexual relationship, or even a routine. Stendra's 15 to 30-minute activation time, however, fits better with the lifestyles of casual daters and more spontaneous types.
It also takes some of the guesswork out of that important decision: whether to pop the pill in the first place - and leaves less time for things to go off the rails or for your partner to lose interest before the main event begins.
In any case, at this point the drug's maker, Vivus doesn't pose much of a threat to the Viagra empire. Analysts project annual sales for Stendra to be $300 million next year, compared to the $2 billion Pfizer netted in 2011 for Viagra sales.