The quality of the envelopes is for this price really very good! Stable, tape sticks well, window well secured!
All in all, here is the value for money really good! (Ca.4,50 when buying)
Conclusion: Buy !!!!
Update October 2014:
The envelopes are now almost 4 years old. (I still have any left.)
Tape sticks still very good! Another reason to recommend this!