Hi! BTF rings are tough for sizing due to the open shank. Typical rings have a closed shank (e.g. round circle), but BTF rings are open. To add to this complexity, the open gap varies by each ring design. The gap is wider on my Frivole BTF ring vs. the butterfly ring. I do not have the Magic BTF ring, so unfortunately, I cannot compare for you.
Here is my sizing to help out:
Normal Rings size: 53
Lotus Ring: 53 (even though VCA categorizes this as a BTF ring, it is a closed circle, so I took my usual ring size).
Frivole: 52 (gap is more open, so I took a size down. I could even wear the 51, but it a bit too snug for me over the going knuckle)
Butterfly: 53 (gap is more closed than Frivole, so I prefer my usual size)
These rings are not resizable, so I would suggest you order both sizes to try on to avoid regret. The sizes do not have to be the exact stone combo; it's more for comparison. If you can only get one ring at a time, get the smaller one first as a process of elimination as the larger one will always fit.
I share this because in purchasing both the Frivole and butterfly ring, I went back and forth on sizing with both rings as both sizes fit me. I kept trying them both on and splitting hairs which I am glad I did.
It's more a matter of which size you prefer. I went with the larger size for comfort. This is especially true if you have knuckles that are a bit large (or might get larger with age. My knuckles have definitely grown!

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These rings, due to their design, will not fall off like a thin wedding band might. For me, my greater worry is they will be tight to put on and off, especially in the summer when it's hot.
Congratulations on your soon to be new ring! Please post pics if you wish! We love to see rings!