We have a 360 and it was retro-installed for free as it was still under extended warranty. I know it was intended to minimise the fluctuations in print length over multiple tiles, but to be honest it didn't make a noticeable difference. It seems to me that the weight of the take-up is only one contributing factor - even when not using the take-up there are issues with panels not lining up.
Unfortunately, there was a massive negative that results from the counter-weight - now the media moves around A LOT on the take-up roll. It seems that the original heavier weight of the take-up bar helped the media run straighter. Without it, the media moves around side-to-side, to the point where, without constant intervention, it'll cause one side to be so much looser than the other that it lifts and causes head strikes, even with the edge holders. With the counter-weights removed, you can let a full roll run overnight without issue.
TLDR, I wouldn't buy them if I had to pay for them, and they were more trouble than they were worth.