Against the right type of player, I'd say it works more like 10 times out 10. Even if they know I'll make big bluffs, when an obvious flush draw out on the flop completes is not the time a tight player is going to try to snap me off. I mean, what does the typical player put you on if you're just calling with two to a suit out there on the flop? The flush draw is always in their mind, believe me. If the flush draw doesn't come and then you bet huge, that's when they're likely to call you down (they think you've missed the flush and are bluffing when in fact you've made the nut straight). But when the flush does come on the river, I'd say a tight player will often lay down a hand as strong as a set. Tight players do NOT like to give action when they think they've been sucked out on.

Again, this is a "trick" play that should probably only be used seldomly (but how often are you going to flop a OESD in a HU pot with two to a suit out there?) and should generally only be used with both a read and position. I'm not sure about the 9/10 number, I just know that the few times I've used this play it's worked, and that whenever I bluff or bet big into a tight player with the flush draw out, they invariably lay their hand down unless they have a flush of their own or they think I'm a maniac.