The only thing is that if the don't have the source machine due to a hardware failure you can't shrink it. We have run into this same issue when using a competitors product as well.
But we have used gparted as well when needing to shrink the original partition past the "unmovable blocks". (transferring a machine from a SATA to SSD drive since the SSD are normally smaller then org SATA)
It would be nice to have a feature in VAW for this!!!