As stated, the PID will hold its temp to a very close tolerence to the set point. How "accurate" it is as far as cabinet temp depends on where you place it. The cabinet temp varies based upon location and how much meat is loaded. But wherever you put the probe, the temp there will be accurate. That is one reason why regardless of the model you get, get the hanging probe not the one that mounts on the back wall.
As said by others, it allows you much flexibility - while the Bradley should not be considered as "set and forget" due to safety reasons, the PID makes setting temps as close as you can get to set and forget.
If it is within your budget, I would get the dual probe. Again it gives you greater flexibility. Could I get along with the singel--yes, am I glad I bought the dual -yes.
Hope this helps