Being a man, a card-carrying member of the clan of man, you might say, I can answer this only one way--there are no drawbacks to dating identical twins, only benefits, particularly if you date them together, one on each arm so that no matter which way you turn you see lovely face. Indeed the only thing better would be to date a quartet of such, so you would be surrounded by the lovelies front, back, side-to-side, while you made your way to dinner and dancing. But lets get back to twins, as I'm starting to feel dizzy imagining everything quadrupled.
Twins are, in my experience, similar enough to double ones pleasure, double one's fun, by the physical mirror-effect they possess,but on the psychological level they are inevitably unique and independent thinkers. This makes for wonderful conversations, and with the gals being two-sides of the same coin so to speak, it's a heads-you-win-tales-you-win scenario. You can look at it this way: no matter what you say, at least one of the twins will agree with you (if the other disagrees) so you are always in the right by way of the same woman--a paradox if ever there was one. Not that twins are clones, other than in some biological sense, but rather they are, if they are date-companions, attractive (at least to you) and hence you have an attractive woman always agreeing with you, even if it is a different woman who is at the same time, in some sense, the same woman. What could be more wonderful All men will agree with me.
Now having said there are no drawbacks in the beginning of this answer, I must admit, I lied. Everything has drawbacks--but I'm having too much fun imagining the benefits. Twins with benefits is not something I would reject easily.