These do the trick as long as you don't need a privacy tint/pattern in the paper. The self-sealing flap has varied in quality with different boxes I have purchased over the years but it has never been a real problem. I still keep buying them.
Since I've done 3 mass mailings a year for the past 30 years I've come to the conclusion that the final step of sealing the envelope by removing a peel&seal strip or by wiping the glue strip with a sponge bottle designed for that has little to recommend one way or the other. I have a little glass dish with a sponge fitted in it for one-at-a-time usage. The main reason for buying peel&seal envelopes is that I need to replace all 3 of my wifes boxes of envelopes (like me my wife has several accounts).