Well the Up-B substitutes for a jump, while actually Jumping negates your first momentum cancel, using Up B you can rise toward the corner DURING your Bair and the Bair seems to act like a bucket break. My original idea was to use Dair since we hit a brick wall if we use it during an Up-B, but Dair was way too slow.
I would also like to speculate that our aerials cancel momentum differently during our Up-B, that or Up adds something in the equation that allows the Bair to cancel more momentum than Fair > Bair. I would like to have someone test all this though, I think it was GWJumpman who did the testing before.
I've never died after the Bair comes out, and I've had some close calls.
I'd recommend practicing it in friendlies first though, its a very unique timing.