A few weeks ago I did this conversion with the Zipp kit on a Zipp 808.
Zipp gives you a new axle that slightly moves the hub to give more space to the wider 11sp freehub-body. So you need to redish the wheel, because post-conversion the rim will be slightly off-center.
I don't exactly know about the ebay offer because I have never tried this. I believe there is a trick to machine the 10sp freehub-body making space for the wider 11sp cassettes.
Alternatively you could consider using a Campagnolo 11sp free hub body.
If there is any possibility I would go with what Zipp recommends.
There is more interesting information in this thread:
https://forum.slowtwitch.com/...=zipp%20xdr#p7227151
Zipp gives you a new axle that slightly moves the hub to give more space to the wider 11sp freehub-body. So you need to redish the wheel, because post-conversion the rim will be slightly off-center.
I don't exactly know about the ebay offer because I have never tried this. I believe there is a trick to machine the 10sp freehub-body making space for the wider 11sp cassettes.
Alternatively you could consider using a Campagnolo 11sp free hub body.
If there is any possibility I would go with what Zipp recommends.
There is more interesting information in this thread:
https://forum.slowtwitch.com/...=zipp%20xdr#p7227151