If you get the billows, I recommend buying the $2.99 damper. IMO they should include it with the Billows. Without it there may be too much free flowing intake air through the billows. Probably depends on what you are using. If it is a WSM, maybe this isn't needed. It is absolutely needed for efficient smokers like a WSK or a BGE.
Explore ThermoWorks, the trusted leader in precision thermometers. From the kitchen to the grill, ThermoWorks meat thermometers ensure culinary perfection.
www.thermoworks.com
Some other comments on the billows. I've used it most on my large BGE and a few times on the WSK, and now I will only bother using it for overnight cooks to provide low-temp insurance.
In short, what I'm saying is I don't use it for temperature "control" I use it a safety net.
I set it the pit up with the Billows attached, but without the fan plugged in. I stabilize the pit temp, add the meat and again stabilize pit temp without using the fan. After the pit temp is stable, I plug the billows into the controller and set target pit temp 5 to 10 degrees the current pit temp. What this means is the fan will not run unless the pit temp drops. Since the BGE and the WSK are very stable with temps it means unless I've messed up the fan will not run at all and I can easily sleep through the night and not be bothered with a low-pit-temp alarm.
I've done this for overnight brisket and overnight pork shoulder and not once has a low-pit-temp alarm gone off.
As far as the X2 vs X4, I use all four ports and I'll put a probe in each hunk of meat being smoked.
