I did go with the monitor sub12. Ive done basic setup, and an initial PBK. The sub has met my expectations but fell short of my hopes...
According to my cell phone spl meter, the PBK charts, and my ears the sub12 really starts to work well around 25Hz, maybe a little before. But a long cry off the 16Hz advertized, however right in line with other good quality small box sealed 12"ers and I more or less expected this, but did hope for "real" sub 20Hz extension. The sound quality is great, the volume is there, the slam is ok but not fantastic. Explosions and other loud LFE effects in movies give an ok rumble, however to get a good feeling from the bass in music the volume needs to be cranked, keeping in mind i listen to ZERO electronic music. Im sure in a slightly smaller room this sub would come alive in that regard. I also only have the gain set to about the 10:30 position, so there is more in the sub.
Next steps will be to work on dialing things in a little better, and enjoy untill the upgrade urge strikes again and at that point probably step into a true big boy sub... Or a second monitor sub12, see how I like it given some time.
I may move the sub to the better corner in the room, that corner gives a smoother and bigger gain but can sometimes sound localized however the PBK may help in that regard. That corner MAY help with a little more extension and slam, but not expecting it.