I always get these. You can mail a check out by itself and it cannot be seen. Good way of closing the envelope as well as who wants to lick an envelope any more.
The only problem I had with these envelopes is that the seal adhesive does not go totally to the end of the flap so in a stack the envelopes can have a tendency to snag on each other. I think it would be better if the adhesive went all the way to the end. Otherwise they are great envelopes