Never mind large envelopes, beat-up or baggy envelopes, plastic/tyvek envelopes (plastic mostly on magazines) or anything other than a nice, clean number 10

I'd rate it "not bad" if and only if one is using it occasionally on a clean, firm number 10 envelope with one sheet (maybe two) of paper in it

It didn't cut even those consistently for me (and I do this a LOT), and like another reviewer I had a number of partial cuts