Actually I can tell the light smoke by looking at what comes out of the top vent, but when it gets heavier I can only tell how heavy by looking through the glass in my door, probably because that's what I've been going by for 5 years.
Bear, I assume you know exactly how much smoke is generated by the AMNPS at various points because of your R&D days with Todd. As for me, I can tell you how much smoke I see wafting out of the top vent and I can tell you how it looks when I open the smoker door to do whatever has to be done. It always looks the same to me and that's a nice flow but not an overflow of smoke. But then I spend my time during the smokes inside the house on the computer or watching TV with my trusty ET-733 Receiver right beside me!
I thought I had a problem two smokes ago with lighting the AMNPS. I couldn't seem to get it to stay lit. Only later on did I figure out that on that nice, bright sunny day, during the 20 minute burn before sticking it inside the MES, the AMNPS was producing light but textbook TBS which I couldn't see in the bright sunlight. I was used to heavier amounts of smoke to start off with. Once I figured that out, I inserted the AMNPS into the smoker and it performed flawlessly to the end of the cook.
At the beginning of my first Winter of smoking I was fooled by the smoke coming out of the top vent. It looked like TBS, but it was the same thing coming from my breath hitting the cold air.
I looked through the glass, and there was no smoke in the smoker. My AMNPS had stopped smoking (Cherry pellets!!!).
Bear