Placing an x-ray machine on the opposing side of the subject would harm the subject and you, and functionally be no different than a medical x-ray operated by an unregulated and dangerous person. Also, one of the few somewhat realistic portrayals. In the Prime subseries she can also use this to find enemy weakpoints and track invisible enemies.
X-ray vision mode is bright and white, similar to what X-ray scans look like, and is anything but regular-colored that someone like Superman sees in. However, like real X-rays, it's stopped by sufficiently dense materials although, Pre-Crisis , only lead stopped it. A power that lets one see through almost anything. Prime 3 lets you kill many tough enemies in a single blow if you find their weakpoint!
Of course, when he tries to see through girl's clothing, all he sees are their bones and organs, like a real X-Ray machine. Hey, did you guys see Power Girl when you came in? Is it possible to make X-ray glasses using any lens or a simple glass? It still doesn't work like it should, though The lack of any kind of contrast invalidates it slightly, but it still makes more sense than the classic comic-book version.