Yup the probe fits right through the air vent hole. I taped the body of the thermometer to the top of the Brinsea so that I don't have to keep threading the probe into the right place when I want to check on the temps. I turn the Spot Check off between checking to save the battery. It works great!
I have the Advance model so there is a digital display on the top of the bator for temp/humidity. I am assuming that what is sensing the temperature is inside of the top part. What I have found is that the temperature is about a degree warmer at the top of the bator than it is down by the eggs. I had to adjust the temperature on my unit to 100.6 to get the temperature to 99.6 at the tops of the eggs. Once I did that, I haven't had to adjust the temperature again. The first time I hatched eggs, they started hatching a day late and finished hatching on day 25 since the temp was low the whole time of incubation.
ETA - what part of Maine you from if you don't mind me asking? I grew up in Yarmouth until about the age of 10 then moved to MA.