I thought I'd jump in with this, as well, after having a weekend to try the sub-1200 out (ordered it the same day as deboardfam).
To start; a general rundown on my setup.
Receiver: Denon AVR-891
Fronts: Polk Monitor 50
Center: Polk CS1
Rears: Klipsch Synergy B2
Sub: Dayton Audio Sub 1200
Wiring is 12 AWG stranded copper, max length run ~ 25 ft. Room size is 10x13, so it's on the small side of things. Crossover/LFE was set to 100 HZ on the Denon, with sub crossover left wide open.
Audyssey was run after setting things up, only to find my coax cable was bad (brand new, center conductor dead). Replaced with several RCA wires. Ran the setup again, sub worked, but sounded quiet, so the gain was upped to 5. Started listening to music, mostly alternative bands (Model Engine, Poor Old Lu, Yngwie). Very good, balanced responses.
Then I fired up the first few minutes of Lethal Weapon 4 (first movie I could grab that I knew of having explosions) not too bad, but it still felt weak. In went Star Wars Ep. 4. Deathstar was..eh. And then I hit a scene of Millenium Falcon cruising by, and the couch was shaking...at 3 AM.
The sub seemed really timid at first, until especially bassy spots hit. It holds music well, and definitely accents the kick drum more vs. no sub.
My previous two subs: Polk PSW505 and Klipsch Promedia 5.1 dual 8" unit with replacement plate amp. The Polk was always very, very subtle, and didn't seem punchy enough, but it would resonate nicely. Never really felt like it was going to really hit hard, beat my face off, or otherwise felt very active. The Klipsch just wasn't big enough for the room size, although it seemed better than the Polk.
Sub-1200 shakes the house way more than the Polk, with the gain sitting at 4. Anything beyond that is going to anger the neighbors. No sign of port chuff, and I have medium-high carpet. Drywall walls.
I haven't broken the sub in, aside from watching a few movies over the weekend. For the price I have zero complaints, and the shipping also was fast (had it in about 20 hours post ordering) with economy shipping. Perhaps the BIC I was considering would have been louder/better, but for half the price, the Sub-1200 is not half the sub. Yes, it's budget..but it works.
As for cabinet shape, the rounded vertical edges are nice. Box feels way more solid than the Polk, with less resonance/vibration. The speaker grille reminds me of how guitar amp and PA cabinet grilles are designed and attached. I have no problems with the velcro or the ring/fabric design as such. In a household with young children or pets, I can see how it may be problematic. I did not open the sub up to look inside, but it's at least on par mass-wise as the Polk, but just feels more solid. I had opened up the Polk at one point to do a slight cleaning/repair, and it just seemed very flexible.
Overall, I'm a happy person with the purchase. Time will tell about reliability, although no sign of the plate amp getting warm, or warm/hot air passing out of the bottom port, so this at least bodes well. The Polk would get decently warm just sitting at on (something the Sub-1200 does not do, even after leaving it on overnight). The Klipsch..well...its original plate amp was not reliable in the least, and was hot after hard use or very warm after sitting. Generally Bash amps make me run away due to poor design in regards to overheating (my opinion after having repaired a couple). Again, it's not the be-all of subs, but is a solid upgrade from a Polk PSW505, and for less than half the price.
One thing that did grab my attention in a negative way: auto-on function. It flat-out did not work for me, and stayed off, regardless of signal level to the sub. My answer to that issue, and to save the switch on the back: socket switch. I just leave the sub switch on, and turn it off at the socket, effectively unplugging it. Auto-on would be nice, but it isn't a requirement, and even finding a replacement socket switch is a $3 fix...not a big deal in the grand scheme of things.
Verbose reply over.