IMHO an A4000D is much more sensible if you dont want multiple 5.25" and 3.5" hardware internally mounted.
The A4000T is a bit of a monster, yes its gigantic but in comparison with a typical PC big-tower it can not take nearly as much 5.25" and 3.5" hardware. The case is strange IMHO, it is designed to work as a desktop and a tower (that is why the two 5.25" units are 90 degree turned).
Though I can understand why it was popular in professional environments where a heavily loaded Amiga was running 24/7, I guess if thats what you want to do an A4000T is a great solution. For myself a loaded A4000D is plenty fine
