Some people like the aesthetics but the cube shape presents problems when stocking due to the shape. A shorter overall tank means you can't stock fish as big as you might in a more conventionalally shaped 60 gallon. I find they are nice if you want to do a nano tank but have a larger volume tank to put the nano fish in. Then they're great because you could have a big school of nano fish like Ember tetras or the like.
I believe he is talking about using the 60 gallon for saltwater.
I have a 35 cube and it doesn't take much room while still being big enough to stock a handful of fish. A 60 cube will give you a bit more options for stocking than what I have. You could do a dwarf angel if you don't plan on keeping coral. And if you want to make it a reef, you'll have plenty of options (watchman gobies, firefish, clowns, chromis, hawkfish)
As mentioned it does somewhat limit your options. Arguably the most important dimension for saltwater fish stocking is the length of the tank and cubes tend to cut that short. Height and width are important as well to an extent, ideally though if you want a decent variety of saltwater stocking options you are going to want a tank with at least a 4 foot length. As for the dwarf angel, I would still go with a pygmy (particularly the cherubfish) as a regular dwarf would still be pushing it a bit. If you have any ideas about a tang, butterflyfish, Foxface/Rabbitfish, large wrasses then you will definitely want at least a regular 75 gallon tank.