The odds of hitting an open ended or double gut shot draw are very close to that of a flush draw (1 out less). I don't like to do this very often as I play low levels, where people tend to make a lot of loose calls and too many people are generally in the hand but, IMO these are good hands to make a semi-bluff with. Still, as long as you have the best hand when you call, you are almost always the favorite and if not so, it is generally not much more than a coin flip. And if they don't hit the turn, you will be the favorite going into the river. In the long run you will win more often than you lose.