I’d be very surprised if it was to become taller. I’d have to watch the clip again, but I only recall seeing the device stretching his pants on one leg.
I know they’ll do it to fix leg length discrepancies above a certain threshold, especially if the other procedure isn’t viable. I don’t know if there’s other medical reasons to consider it.
That’s my understanding of the procedure as well. The other method requires more prep but is quite easy.
If they catch it early they can measure how fast each leg is growing at 6 month intervals (and other measurements). Then they can go in and tell the longer leg to stop.
That procedure can be close to painless. A month with a soft cast and crutches, another month with just crutches, and a third month with no physical activity.