My Kraahkan arrived yesterday in great condition: This mask is amazing! The one I ordered was Black Strong & Flexible, and while it is certainly strong and black (although not quite Lego's standard of black; this is more rather very, very dark grey), I'm not going to find out if it is flexible! The grain is minuscule, with only a tiny amount of fraying on the "jaw-line," but it's nothing very fine sandpaper can't fix.
The only gripe (and it's a small one), is that the axle holes are loose. While the hole located on the mouth can just about hold a 2-length axle, the axle hole on the top is very loose: axles fall straight through. This is only a real problem if you are not used to making custom heads, or want to use a Metru head for model-making. A good solution is to either use an axle with a 'stop' at the end (either the 4L with a smooth stop or the 3L with the stud stop), and a bushing on the inside. This will keep it securely in place and leaves enough room for custom head making.
While 3D printing is a relatively new commodity, it has to be said that this is an amazing design and print, and an essential addition to anybody's Kanohi Collection. 9/10!