It's hard to base my comparison against other steel chassis', as they are much easier to make them do what you want and with fewer rules to follow than acrylic demands. That in mind, I tried to be as fair as I could, but still keeping in mind what else is out there for the price. Speaking of, let's get that over with now. The Black-Series Tower 21 lists at Danger Den's store for $279.99 base price. I say base price, because there are a few things that you can change. Color of the front and back, removal of the fan grills, or possible custom ones, or the Novus cleaning kit to ensure a fingerprint free experience can all add to that price. We haven't even gotten into the custom etching that is possible through Danger Den either! I'm sure if you want to go all out you could end up with a chassis nearing the $400 mark, but it will be completely customized as per your request, as long as it fits in with their requirements.
Pricing out of the way, we can get a real effective look at things. Roughly $300 puts you in the league of the Obsidian 800D and Lian Li's and even most SilverStone choices. Those are superb offerings, but lack customizability from the manufacturer and the pride of accomplishment; nor do they offer the view the almost invisibility Black 21 has. With that said, there were some issues. First and foremost was the lack of hardware. I'm sorry, but this is a big thing to me, especially at that price. I would assume it happens, but for $300 I expect someone to know how to count. Dust, wow, the dust! I have an older home and it is prone to being a bit dusty at times when the furnace is active, but this thing was so statically charged from peeling all the protective coating, it was a magnet for everything floating within 5 feet. I would assume wiping it down with the cleaner that is optional may correct this; I really don't know. This is my first acrylic experience. The last thing to bring up is more for a personal reason, but one that you may not have thought of. This is not a tinkerers chassis, as getting inside isn't as simple as a couple of thumb screws and badaboom, you're in. You need gloves and a screwdriver and about 2-3 minutes just to get in, so be sure before you close up shop, things are stable and permanent.
In the end, I have three words of advice if you really love the looks and desire to obtain the Black-Series Tower 21. And those are patience, planning and some more planning. The chassis is a real looker and a well laid out design, just once it is assembled, sometimes it is already too late and you need to remove six or eight nuts and bolts to correct the issue, like trying to install the front case fans. Things like a modular PSU, where you plan to run the wires, or even how you may want to hide them needs to be addressed, because with the almost 360 degrees of visible access, there is no room for shortcuts or haphazard wiring without detracting from the build inside, so keep those things in mind. Even with pieces missing from the hardware and things that if I did the build again, I would definitely change, I can see this taking a normally great rig, and making it a truly outstanding show piece for all to admire. You just may need to get bibs to keep the drool off of the case.