The oil pump and balance shaft assembly are one unit, hence the price.
'The internet' says it's a common failure (as it always does about everything) but there isn't enough hard, unequivocal data to back it up.
The only acknowledgement from VW was a recall on VERY VERY early EA113 engines because the balance shaft sprocket liked to fall off. I think they changed the nut/washer on it or something.
The only community speculation on it is servicing regime (oil change frequency, oil quality, oil level) and tuners extending the rev limit past 7500rpm, which over spins the balance shaft. I think the shafts just run in plain line bores like the cams, so any excessive heat won't be welcomed.
Take from that what you will, but there's no point replacing a £1000 part just because it might break.
