I know this is old but I just wanted to post the results of having tried the aspen pellets again.
Basically, my opinion still stands as far as the aspen pellets being a poor bedding for rodents. I had changed out the Good Mews pelleted paper bedding with the previously mention Green Pet "Aspen Supreme" in my FB rack. I had to change it back a few days later. The odor after just 2-3 days was worse than Good Mews at 2 weeks.
The aspen pellets broke down and turned into dust which got compacted in one corner of the tubs. The Good Mews holds its shape really well and doesn't deteriorate anywhere near as fast as the aspen did.
I had actually left one of the gerbil tubs with the aspen in it, and I could still smell that ONE TUB. I think it must be influenced by personal preference though, because I can barely stand the smell of the aspen pellets when I open a new bag of it. For some reason it reminds me of ferrets.