Received these screen protectors free as part of the Hardware Package Amazon were doing for the 3DS, and I have to say I totally disagree with the previous two 'one star' reviews.
The protectors are a nice thickness and while there isn't an applicator card supplied, you can use the edge / corner of a credit card or something similar. Just to note a credit card is too large for the touch screen but I just tilted it a bit and it was fine
Sure, fitting screen protectors can be a bit fiddly, but you need just need to take some care.
Line up the screen protectors first, so you know how they will fit - practice the motions described below if you're unfamiliar with applying them
Prepare in a 'dust free' environment - some where like the kitchen where you won't get a load of carpet fluff stuck to it
Clean the screen with a soft cloth ensuring no dust remains
Peal off the first film (tab 1) and line up one end (I find it easiest to start on the left side but I am right handed), then using a piece of card push this along the surface of the protector (e.g. left to right) whilst gradually lowering it onto the screen with your other hand.
Use the card to push out any remaining air bubbles or using a soft cloth rub in a circular motion from the centre outwards.
Only once you are happy there are no air bubbles left and it's all stuck firmly in place then remove the second film (tab 2).
With a bit of time, preparation and patience you shouldn't have any trouble. I certainly didn't and for free I really can't complain!