Will 1-inch panels actually reduce echo?

Yes, mostly in the mid and high frequencies, which is where slap echo and harsh reflections live. They will not do much for deep bass rumble; thicker panels or corner traps handle that better.

Do the panels stay stuck to painted drywall?

The peel-and-stick backing holds on clean, smooth, dry surfaces. Wipe the wall first and press each panel firmly; dusty, textured or freshly painted walls are where adhesion tends to fail.

How much wall do twelve panels cover?

Each panel is roughly one square foot, so the pack covers about twelve square feet. That is enough for a small booth or a few reflection points, not a whole large room.

Can I cut them to fit?

Yes. Dense foam cuts cleanly with a sharp knife or scissors, so you can trim around outlets, corners and window frames.

Where should I place them for the best effect?

Start at the first reflection points beside and behind your listening or speaking position, and near doors and windows where outside noise comes in. Spreading panels out beats stacking them in one spot.