CoolerMaster's Stacker 830's already has a long list of features, and it's hard to see how more can be added. The Stacker 831 has a few extras.
The main point is the aluminium build. The case appears deceptively chunky and unwieldy, but is lightweight for its size. This has the benefit of better heat conduction but this adds to the price.
Then there are the cooling options, the case has support for up to nine 120mm fans; four of these can be attached to one side of the case. An inlet located at the bottom draws cool air in, while you have the option to mount the PSU vertically or horizontally, whichever provides better airflow for your setup.
A big feature is support beyond ATX motherboards, including BTX. This smaller form factor completely rearranges the layout of components, improving thermal efficiency and alters the mounting points in a case.
The Stacker 831 gets around this problem by allowing the case to be taken apart, then reconfigured with the addition of a BTX upgrade kit (requiring a small additional outlay). This is an ambitious feature, and one look at the instructions could turn the less experienced user away.
The appearance is attractive and doesn't offend with garish features. Aspects such as the power button along with four USB ports in a black indent at the top. The door and case are decorated with a black lattice guard, that looks good and still allows air to flow through the system.
Installation is defined as tool free but not it's easy. Granted, the side panels and tray can be removed with clips but fitting a hard disk involves removing the 4-in-3 device rack with a screwdriver. This process was more complex than it needs to be, and not as intuitive as other removable 3.5in bays we have seen.
The lack of bundled accessories means no value award. Only two case fans are provided, the BTX upgrade kit is an additional expense and the cross flow fan is optional. But, with the sophisticated, funky look, you can fit a ton of drives into it and it can push through a lot of air. Well worth it.