Unlike traditional multi-booting, where the other partitions aren't hidden - I was left with five drive letters (C,D,E,F,G). The primary Windows installation stays as the boot drive, and entries for these other installs are kept in boot.ini.
Switching between installs is just a matter of rebooting. When you boot in to one of these Windows installs, the drive letters don't change. Some software is badly written and doesn't cope particularly well with installation drives other than “C”. So this is something to be aware of.
For instance, Daemon tools wasn't happy at all. Although in some cases, it can be useful to see the other partitions, for instance if repairing an install, as your documents should be on a separate partition, I would have sooner seen the partitions invisible to each other and all labelled “C”.
How you decide to use HyperOS is entirely up to you. For instance, you could have a separate Windows installation for every family member. Or, you could keep your main Windows installation, and then a fall back copy that can be used for repairing the primary copy, or even for when you are on a deadline and just need any copy of Windows to get your work finished.
Quite simply, this could be used as a backup tool, with extra benefits. For myself, I would make a clone before installed any new software.
Another issue with this software, is its dependence on the primary installation of Windows. By having this as a the primary boot partition, it means you are never free to delete that partition entirely. However, when restoring a backup – the backup only contains Windows/Documents and Settings/Program Files, so only these folders are replaced. So there is no real need to actually destroy the partition. However, there are some cases where clearing the partition would be useful.
As seen above, it is also possible to not restore the Documents and Settings folder (which contains My Documents and your Desktop for instance). This is good to know.
Overall, I was pretty impressed with HyperOS. I didn't run in to any major issues (aside from Daemon Tools) and in the right hands could be a very useful utility with many different applications. I do feel that you do have to have a good sense of what you are doing to make the most out of it though. I also feel that in many scenarios, Norton Ghost would be better suited and this is not a direct replacement for it.
This version was the Geek install that allowed up to 11 installs and is priced at £29.00. There is also a version priced at £19.00 which supports up to 4 machines.