If I get the VMS unit from this info I won't add Ozi to it, thanks for the info.
@Heidi at OziExplorer is a mapping application that can run on Windows or Android devices, but it doesn't come with maps, so it's a little misleading to say that a particular system had better definition maps than Ozi.
You can buy many different map sets to use with Ozi, and the accuracy and definition is therefore dependent on which maps you buy.
As a stand alone product it's very economical and allow you to run almost any map set you like.
The one thing it doesn't do is turn by turn navigation. This is the reason I run multiple applications, and I then use the one most appropriate to the task.
@Drover is correct saying you should avoid anything that solely relies on an internet connection for its maps, however the hybrid products such as hema explorer are a great comprise with the ability to both store maps on the device, and then further enhance them if you do have internet connectivity available.
If you just wanted to use an iPad, you could use a combination of hema explorer or hema 4WD with another app called Metroview and you would have a very powerful navigation suite for about $70 that did everything you need.