What, you haven't opened it already?

If the flaps aren't totally stuck down, a letter opener or sharp knife won't ruin the whole. Ya gotta love that seal used on the back!
Like the typical packet, the best stamps are usually going to be in the front window. Expecting cheap stamps, I don't think you need to worry about forged overprints. Now if you find postally used forgeries, that's another story.
The good "packets" were the souvenir booklets made up for tourists during the 1960s, usually small brocade covered stock books with glassine strips. They typically had mint stamps. Since those stamps have skyrocketed in value, there is typically some money there. But they never had complete sets or the key high values.