AFTER releasing it? I figured the idea would be to PREVENT the finishing animation of whatever move when you jump. Not trying to sound brash, but that doesn't sound like a legitimate Jump Cancel to me. Why the need for magnet release first?
The release hitbox is only out for one frame, and you can jump as soon as the hitbox is gone, so you do prevent the entire endlag animation of the magnet by jump cancelling. This is even better than jumping out of shine, since shine hits frame 1 and can't be jump cancelled until frame 4, so you have 2 frames that you can't jump compared to 0 with Lucas (not counting hitlag in either case).
Incidentally, I'm confused about how Lucas's magnet hitboxes actually work. When I hit someone it always registers 2 hits and does 8%, indicating that I'm hitting with one loop hitbox and the release hitbox. Does anyone if they both hit on the same frame, or does one hit before the other? If they do hit at different times, what frame does each hit on? I'm pretty sure the first hitbox can't come out until frame 5 since it wouldn't be possible to b-reverse otherwise, and I assume the release hitbox can't hit before the loop hitbox because the opponent still takes knockback. So does that mean the release hitbox is actually on frame 6, or do they occur at the same time? I've only examined this in training mode, and the two hits register sequentially, but I'm not sure if that's because they actually occur on different frames or if that's just how training mode's hud works.