Backing up or snapshot VHDX diff disks in a SP2013 test farm

Hi community 

I have been using Win 8 Hyper V, to build a number of SharePoint 2010 and 2013 test farms.  Essentially, set up a windows 2012 parent disk with some common stuff such as all the browsers, fiddler and ULS logger.  Thereafter,  I can reference my parent disk when I create my individual child diff disks(  New-VHD). Now I am able to  install SharePoint 2010 or 2013 without the hassle of having install the operating system each time.  

Now I want backup these diff disks ahead of testing a CU or other farm changes, so I wondered what is the best approach here:

• Use Hyper-v snapshot facility: how many of these, how often, and how reliable are these? Also, if I need to backup my snapshot files is there best practices here as to which ones I need to backup
• Go for physical backup of the my hyper-v: VHX and config  files and if so what are the key files to backup. I had look at my spdev installation (see attachment) and there appears to be a load of related files – how are these created and do I need to back these all up.?

Daniel