To gain access to the interior you may remove the two side panels as a first step. This gives a good view into the interior, allowing you get a sense for where everything is located. The motherboard tray divides the top and bottom areas, with the latter being for storage and power.
The motherboard tray has a cutout below where the CPU cooler will sit, so you can have some basic access to the backplate, even in such a configuration. The four expansion slots are in a traditional position, allowing you to fully use every expansion possibility of an mATX board. The rear facing side of the 3.5" HDD cage may be detached by removing a total of four screws - two on the top and two from the underside of the case. While this eliminates those drive bays, it will allow for large PSUs to fit and still gives you a remainder of five 2.5" drive bays. The rear 120 mm fan placement is also at the usual position for this type of layout, right behind the CPU socket.
The external expansion bays are pretty straight forward, and Chieftec includes a tool-less locking mechanism on one side, but not the other. It is made of some very flimsy plastic and as such our recommendation is to just omit this. The target audience for this case won't care for this at all and would likely just want to use normal screws to secure an optical drive instead. Noteworthy here is the fact that the CI-02-OP also provides a single 2.5" drive bay below the 3.5" one, which is a very nice touch.
Below the motherboard tray, you will find two cages for drives, one for 2.5" ones and another that allows for both 2.5 or 3.5" variants. The smaller variant may be removed from the enclosure to allow you to fit drives outside of a crowded interior. Considering the two floor placement possibilities, the Chieftec Pro Cube CI-02B-OP provides room for up to seven storage drives, which is most excellent, and could cater well to those who need all the storage they can get in their professional work environment. Another small but important feature are the small holes for zip ties along the one edge of the motherboard tray. As we will see later on, these will come in quite handy.
Looking at the ceiling, you can clearly see the mounting holes for either a 120 or 140 mm unit. Chieftec could have easily included a 180 mm mounting possibility as well, but that would mean that you would be a bit limited in the length of your optical drive. Regardless of that limitation, it would have been a nice option to provide users, especially as the chassis comes with no active cooling. Speaking of which, while this is perfectly fine, a case like this is usually used on a corporate/work environment, as such, simply having one or two non-RGB fans included out of the box for a little extra money could be really useful to some potential buyers. Maybe Chieftec could offer a different SKU of this case with such cooling units included in the future.
While most cases these days sleeve their cabling all black, the Chieftec Pro Cube CI-02B-OP comes with color coded case wiring, which is quite alright, as you won't see any of these once the system is built anyways, and they're beneficial for cable identification. The leads for USB and audio on the other hand are sleeved black.