I have the double front and I like it quite a bit. My only problem with it is now that I'm packing with a Mango, the binder kind of gets in the way. I stretch it down into my boxers so it doesn't roll up...anyway, it just gets a little annoying because I have to adjust my binder after I piss. You wouldn't have that type of problem with the tri-top...but I'm not sure it would bind your chest as well. The only thing I would warn you about is this: if the tri-top rolls up the same way the double front does, you're gonna get pretty annoyed with it. Rolling up means discomfort AND less tightness, so less of a bind.
It doesn't make me COMPLETELY flat...you're still gonna want to stay away from some fabrics. I don't think anything is going to make you completely flat (other than surgery). But it definitely helps. I don't actually know how big I am, but I'm pretty small. Binding also helps to make your chest less...cushiony. So it's no longer a dead give away when you hug somebody.
A really great thing about binding with an Underworks binder is that you get to the point where you don't even notice you're wearing it. That doesn't mean they're comfortable...but it does mean they don't hurt you. You bind with an ace bandage or something and it squeezes and pinches and gets in the way.
Oh, and I recommend stepping into your binder like a pair of pants and pulling it up. They're really, really hard to get on if you act like it's a shirt. Take it off like that, too.