I found these a must, especially for the touch screeen as with the normal DS, the screen ends up going through it a bit!
When these are on, they are great, easy to work out any air bubbles which is why it has three stars. However, I did find that it was important to be quick and not take the first layer off then leave it for air to get to it...i am talking seconds!! Because if this happens, dust gets on it and each speck of dust creats an air pocket which is impossible to get out. Not noticable once the screen is on, but i am a perfectionist and hated it! Only a niggle though, and I also found cheaper ones out there that did the job too! so all in all its good...but not that good :)