Self-adhesive saves lots of time. The price is considerably higher than I would like. I heard [...] has the same quality at about half the price. I'll check it out!
These are more expensive than regular lick-to-seal envelopes. For your everyday use to send one or two letters I wouldn't bother. I bought them when I had to do some small mailings for a business -- about 50 letters at a time. Licking 50 envelopes will really wear out your tongue. I've used sponges in the past but this is a lot more convenient and less messy. (I always get damp table-tops and damp letters when I use sponges even those designed for moistening envelopes.) If you're doing large mass mailings hundreds or thousands of pieces the extra cost might add up. I guess that depends on your budget and how much you're paying the people who assemble the mailing. (My big mass mailings have always been for non-profits so we were cutting pennies everywhere.)