Ok, so I have had my WSCG for two weekends now and have done 4 cooks. What I can say is this:
1) once you get the temp dialed in, it is rock steady. I had a 3 hour spell on a 6 hour pork shoulder cook where the WSCG held its temp +/- 1 degree for nearly 3 hours. No ATC.
2) it does have a high thermal mass, probably not as high as a ceramic, but on my initial cook I over shot my temperature by 150 deg F. After I shut all vents, it took 45 min to get down to my desired temp range.
3) the ATC (BBQ guru DidgiQ dx2) was easy to set up, initially it over shot the target (think I need to manage the fan damper), but then kept steady temps overnight.
4) it's very efficient, I ran a 15-17 hours brisket cook and only used about 1/3 Kingsford blue (19 lb bag).
5) if you are planning a low and slow cook, be careful with how many coals you start, or how long you keep the gas assist on, because it is so easy to get a temperature excursion.
6) I love the two tier charcoal grate setting. I keep it on lower setting for smoking, I keep it on the higher setting for higher temp indirect/direct cooking.
That is what I have learned about this beast so far.