I have used dd in a similar way to preserve small drives like the SSD on a netbook. (8GiB)
I would not recommend using dd to bit copy a drive larger than 64GiB for two reasons;
1.) You need a receiving drive with either the exact amount of available space or much more space than the drive you're copying.
2.) It takes forever!
Furthermore, When I upgraded to Windows 10 the first time, Microsoft provided a roll-back option that's available for thirty days after the upgrade. I may be wrong, but I think this is available as a standard feature of the upgrade.
P.S: the dd command I use to make a 'backup' of a drive is;
sudo dd if=/dev/sda of=drive.img bs=1M
In order for this to work, you have to navigate to the directory where you want the backup file saved and /dev/sda must not be in use at all. (so boot from a liveCD to do this)
To reverse it, just swap the if= and of= but beware that everything in the of= path will be overwritten and stopping it once you start won't save your data. (it starts overwriting immediately. Hence the nickname "Data Destroyer")