As slip cases go, those do look very nice, although I'm wondering what the inside material is, and I can only find two Bugatti Skinny case reviews online in total, for any phone model. (Both positive, but two reviews is near-meaningless.)
Seems a bit beside the point, because I can't find anybody selling Bugatti Skinny cases in the US market, and the only European seller on Ebay wants ~US$50+ shipped, which is insane.
Edit: I should also note, they're not specific to the One X; they're generic cases, and there seem only to be three sizes in total. Note the list of compatible models with the same case as the One X, and how much the size differs. There's an 8mm difference in length between the smallest and largest, and a huge difference in girth (the Razr XT910 is only 489mm square; the Sensation and Titan are 700mm square. The One X is the fourth thickest, but at 622mm it's quite a lot smaller than the Sensation and Titan, so the case is likely going to be fairly loose.)
Motorola Razr XT910 -- 130.7 x 68.9 x 7.1 mm; 489mm girth
Samsung Galaxy I9250 Nexus -- 135.5 x 67.94 x 8.94 mm; 607mm girth
LG P940 Prada 3.0 -- 127.5 x 69 x 8.5 mm; 586mm girth
HTC One X -- 134.36 x 69.9 x 8.9 mm; 622mm girth
HTC Sensation XL -- 132 x 70.7 x 9.9 mm; 700mm girth
HTC Titan -- 131.5 x 70.7 x 9.9 mm; 700mm girth
Sony Xperia S -- 128 x 64 x 10.6 mm; 678mm girth
To sum up: The One X is the second-longest of the bunch, and so quite likely to stick out the end of the case a bit, unless it dwarfs the smaller phones. The largest phones have 12.5% greater girth than the One X, so the case is likely to be fairly loose, unless the Sensation and Titan are extremely difficult to get in and out of the case.