Got mine in yesterday.
Went to get some 3Ds XL screen protectors and accidentally got two doublepacks...
Ended up fucking the first protector up quite hard.. I tried cutting it with a really sharp knife, didn't work that well and went off course.
The second one I cut with one of those paper cutters (which neatly align the paper). The touch screen was a tad too small in the width and the top screen was just really too small...
For the third one I used the "upper" layer of the second screen protector and made small adjustments by hand, this one ended up being fine
Only 2/3 airbubbles and one dust particle, so I'd call it a success, as the are invisible during use.
Tip for other people wanting to do this.
Also get a sharp knife (carpet cutter, or a stanly knife) with replaceable blades and use it to cut small edges off near the corners, to get the same rounding as the screen itself (cut it before placing it on the 3Ds.....).
For the best result I noted that pressing the knife down worked better than "pulling" it over the protector.