Chocolate: difference between "Cocoa Mass" and "Cacao"?
Yep, cocoa and cacao are the same thing.

The 72% has sugar making up the rest of the mass. The description on amazon actually mentions that it's 27% sugar and 43.5% cocoa butter. The rest is cocoa solids, the chocolate-y stuff. As you say, that particular brand is pretty expensive; it's also pretty popular and well-regarded. Since it has plenty of sugar in it, you can use it for pretty much anything, including things like coatings, or even just eat some.

The 100% is unsweetened (there's no room for any sugar in there) so it's really only usable for things like baking, where you'll add some sugar. It's unlikely to be pleasant to eat on its own.

For what it's worth, usually in English you'll hear cacao only when referring to the overall cacao seeds and their use as a component of chocolate. It's not common in non-culinary contexts. For example, we'll say "cocoa powder" not "cacao powder".