I buy Forever Stamps. Still valid for First Class regardless of postage rates. Rates aren’t going down, so you can’t lose.
Folks I know bought 1,000 of them - they spent $420 in order to save maybe $20 over the span of however much time it takes to use 1,000 stamps.
The streamlined, no-hearings-necessary postage rate increases that we’ve been seeing are simply tied to the rate of inflation, so in effect, the Forever Stamps are simply a bearer instrument indexed to the rate of inflation. You’d do better paying cash for your stamps at whatever rate they happen to be at and sticking your $420 in a money market account.