How do you know when it’s full?
Part of having the bag on mine is being able to see when chips are getting past the cyclone because it’s full. (like now, actually… Kinda amazing how many chips you make processing rough 8/4 lumber into useable sticks)
I just lift it. I have never let it get past half full.
What you need is a weight sensor under it to light up a “go/no go” sign 
Mine’s new enough that I haven’t had to empty it yet. I’ll do a “lift” test, and I expect I’ll hear a difference in sound if the barrel gets full enough that the Thien baffle allows bigger chunks to end up in the bucket under the filter. I may add a manometer (colored water in a clear tube) to the filter at some point.
You can’t see it on mine because of the sawhorse leg, but I put a window in the barrel.
I was thinking about putting a window on mine.
I thought about it. But the lid is also easy to remove.
Maybe if I get bored one day.