I've tried the Elegant Suit for cheating at poker and discovered that it is really hard to consistently cheat and not get caught. Playing without cheating is reasonably profitable as long as you play tight (sometimes you can spot patterns from the other players too), so is cheating really worth the effort? Do you gain that much more from cheating that makes it worthwhile?
In order to unlock an outfit later in the game, you have to eliminate all of the other players in a game at Blackwater. Cheating sure makes doing that a lot easier. It's also not as hard as I thought it was. I tried it a few times at the beginning of the game and decided it wasn't worth it at all. But when I was working on unlocking that costume I decided to give it another try and realized I was way over thinking it. It's not quite like breaking a horse where you essentially slam the stick from one side to the other. Keeping the arrow in the middle for cheating actually takes a little finesse.
The NPCs aren't that good at hold'em so if you have some poker knowledge cheating isn't really necessary to bust the NPCs. With that said it takes a while and can get really boring playing long enough to eliminate everyone from the Blackwater game for the outfit.
The way I did it was to cheat, get caught, kill the accuser in a duel and then get back to the table as soon as a single NPC sits but before the other two get back. Now you're playing heads up which is much faster / easier and you still credit for busting everyone.