The Duraflexi protector is made from TPU material, part of the reason I chose this is from my previous experience with TPU cover for smartphones. The material surface is in between a smooth surface like polycarbonate (slippery) and silicone (high grip). Perfect because you don't lose the grip easily AND it doesn't feel like silicone, where it's hard to put in and take out of pockets/purses/bags and collects lint/hair. It is also in between as far as flexibility, not stiff like polycarbonate and not limp like silicone. Very easy to slip on the 3DS XL and it doesn't fall off once on. It's also low profile, it does not protrude out much like some other protectors.
Perfect type of protector for our family. We mainly wanted some protection from a slight drop (low height), protection from dirty/oils from hands, and protection from scratches. This fits the check list. It does NOT protect the two buttons on the corners so if you need/want full protection, do not buy this one. I can recommend this to someone who maintains their gadgets gently, mainly uses it sitting, etc. If you are rather abusive in handling things, frequently on the move with the 3DS XL, or have active children, I recommend something else, like the NERF protector, for example.
I knew I wouldn't be able to use a similar clear polycarbonate cover AND fit it into the travel case because polycarbonate had a hinge. This Duraflexi protector doesn't and it appears to be pretty slim. I ordered and I can say I am pleasantly pleased that I can still use both the cover and the case. It is a tight squeeze and the way I put it in the travel case is upside down with the buttons towards me. I reviewed the DSi travel case as well separately.
UPDATE 11/3/13: It's still holding well, very easy to hold and slim, one small minor issue is the edge of the corners for the bottom portion 'may' be a little annoying to some users. It is very minor but I will explain; it is right where your left and right thumb areas are, I find it more so for the right thumb. The right thumb hovers over the X/Y/A/B buttons and the A button is very close to the right edge of the protector.
Sometimes when I play, I feel my thumb 'pulling/rubbing/stretching' against the right edge of the protector. Over time, can this cause the right corner bend slightly outwards? It hasn't yet and I do recall touching that edge near the very beginning of owning the protector. I don't recall it much now, maybe I got used to it or it was certain games played.
*** Please see the comment left in this review by another member, that member provides some good information regarding this and other types of protectors.
[...], it will encourage me to continue writing and updating my reviews, and leave a comment if you have any questions, I will be more than happy to answer if I can be of help.