if you get an all in one..........you fill it with water, and whalla. ur done.
you really dont have any room to do different things like add a skimmer, add reactors, change up the lighting etc. with a smaller tank, like a 24" cube, at least you can do some variations with equipment, verses an AIO 29 biocube.
nothing wrong with biocubes, owned one myself for years as a QT tank. they work fine, but you're limited with what you can do with them, unless you start to mod them.....of course defeats the purpose of buying it if you are going to do drastic changes to it.
GL
C