Will this tape repair a broken stem?

withink 48hours it'll probably have a strong enough knuckle to support itself. It'll be stronger than before. the only concern is leaving it on so long that the plant starts to grow around the duct tape or restricted by it. Easy enough to avoid. Try to shape stems before putting the tie in place. No smashing or smooshing vascular tissue.. just bend in 2-3 spots around the corner/angle you want to form. the little plastic trainers are awesome for this, too. tie-downs just hold the form/shape and shouldn't have too much resistance initially.

Definitely worth a shot, but if it starts to really decline just cut the losses and you should be fine. Rest of the plant looks strong and healthy.

Its important that you maintain a tight contact between the 2 snapped stems for it to be able to heal

If the operation was successful those will usually stand back up within 24 hours. I snapped the same stem a second time while removing the tape during my last grow, but luckily it healed both times. I decided to not try removing the tape again which turned out to be fine for me.