I have the bra in a 34DD because that was the easiest size to access. I can tell it's a great quality bra, especially for FOT. I'm a 30-31" underbust and normally wear a 32", but this bra is tighter than a typical 34" and it was silicone grips so I wouldn't be worried about it budging. Although 34DD is sometimes a sister size for me, I'm completely overflowing in a DD. There's overslow all along the cup and it's particularly obvious at the underarm (armpit overflow). It's an occassion bra, so you may be able to get away with wear the wrong size. However, I found this size just gave me mono-boob (bum crack cleavage) the way a tube top would. Overall, try to size up in the cup. Even a 34F would have been an improvement for me.
Tried this strapless bra on in store along with a 30E (I am usually 26FF). The band fits tight, probably most like a 28, but it was too big on the smallest hook. It did stay up though, but I didn't try jumping or anything. The top of the cups curl inwards and cuts in, and I did not get the advertised cleavage due to my shallow boobs.
The bra feels pretty secure it terms of not slipping, but it does feel like my boobs are trying to push it down due to too shallow cup bottoms. My breasts pretty much want to jut out straight at the bottom then taper up smoothly. With a tight shirt the quad-boob is a bit laughable. On the up side, it's all hidden with the dress. Still, I would consider wearing my basque and maybe making a decorative back panel to cover up the part of it that shows in the back. The reason I'm considering sending it back is it's so durned tight. I think I have to start breathing lower in my torso. It's healthier anyway. On the other hand, the lack of underwire is pretty comfy. Too bad it isn't a more open cup style.
This is the first strapless bra that stayed put!! I have it in a 32DD, and have lost weight since (current cup 30D). The cup seems to fit, simply because of its shape, but there's no boob at the bottom of the cup. It used to stay put all night, but I doubt this will happen anymore.
It measures narrow for a 32, but it also sits lower as to give you a lower back cleavage
Bra fits first ok but after a few hours the silicone/rubber band starts to chafe my ribcage. Larger band size might be perfect. Cup size is slightly too small so I suggest you to try one size up there.
Pros: It keeps my boobs tight in its "hands", bra looks nice.