This is a great product for reducing echo or room reverb in rooms with hard walls and little to no textile fabrics. It’s a great start.
I use these in my studio where I record, mix and master. I also have a drum set in this room.
The physics are quite simple, if you want to reduce higher frequencies thinner absorbers like these will do just fine. If you want to absorb lower frequencies you need thicker absorbers as well as measure where these frequencies build up in your studio.
I put them directly on my walls and attached them with glue. This gives a clean look that I quite like. I have used staplers in previous similar scenarios but that does not look as good, and I do not recommend that method.
In conclusion, they will make a difference. The difference may just not be as apparent as you expect. They do not completely block out sound from other rooms or prevent sound from traveling to other rooms.
For me they work great as a transition and will be a foundation for a room-in-a-room studio I am working on.