I alwats purchase "STAPLES" brand envelopes. Even though these have ths strip that you peel to secure the envelope I always tape over it. I do this for added protection
Used the envelopes to mail catalogs. The envelopes seemed sturdy enough but didn't seal well. Just handling them while getting them ready to mail some of the seals come undone. Price vs quality of seal....not a good choice. Will look for something else next time.
Ends of the flaps do not seal down so have to tape the flap to get the post office to accept it for mailing. Glue could be a bit stickier and go all the way to the ends. Nice heavy envelope very little see through sticks better than the dry gummed type.
I bought these self sealing mailers for the convenience but the adhesive was not sticking and I had to use an additional mailing seal to make sure they stayed sealed.