Used this kind of self sealing envelope for first time recently and after getting over initial confusion ("Where's the peel off strip?") I discovered I loved them. Plus no waste--better for the ecology and all that!
I mail a lot of invoices every month & use laser printers and these envelopes are by far the best I have ever used. You don't have to worry about all the problems you have with gummed envelopes (Cut lips or tongues getting stuck together & glue failure) and you don't have the problems of peel & stick ( millions of little papers floating all around.)
While the envelopes are easy to use and enviornmentally friendly they are slightly see through. I can see some of the typing from the documents that I am mailing through the envelope. Therefore this may be troublesome if you are mailing checks confidential documents etc.