They are used for entirely different purposes. Desktop Manager is for (among other things) backing/restoring your data and loading/updating operating systems. ShrinkAnOs however is used on a newly installed operating system to reduce the footprint on your device. It can remove features you will never use thus saving space on the device for other more useful software. In other words if you know you will never used voice activated dialing it can remove that from the operating system so that when you load the operating system to your device it won't be on it thereby saving space.
