To add, it is worth £20 to me just to install and play. No having to do the following.
Install Arma 2. Run arma 2 once. Patch arma 2. Run the patch.
Install OA, run OA once, patch OA,
Verify install for Arma2 as it never installs properly
Verify install for OA is at never installs properly either
Install Dayz Commander
Download Dayz,
Reboot PC
Use Nvidia CP to turn off bloom (if you are lucky and can remember the right setting) so you don't get white trees.
Turn off SLI as it doesn't work with it.
Play.
Buy new SSD because that combo took up 40GB.
vs
Download Dayz SA
Play!