The above comment just goes to show how variable lens QC is. The 24 TS-E has a very ordinary performance according to Photodo tests. My own copy is also very ordinary. The 90mm TS-E scores much higher on the Photodo tests and my copy seems to mirror that performance. The excuse is, the image circle of T&S lenses is larger than that of standard 35mm lenses, which makes it more difficult to maintain standard 35mm quality. The 90mm TS-E, although good (perhaps very good), is not outstanding.
I would expect the Schneider 28mm shift lens to be significantly better than the Canon TS-E 24mm, but I also cannot find any reviews of this lens and I'm also in the dark.
The problem here is with unrealistic expectations. A 24mm lens covering a 35mm frame is a rather wide angle lens. To cover that frame with movements requires an extreme wide angle lens. Extreme wide angle lenses are extremely difficult to design and manufacture. So it's just not reasonable to expect that type of lens to be able to produce images with the same resolution as a 90mm portrait lens or a normal 50. Even expecting the TS-E to deliver the same resolution as a f/2.8 for the 35mm frame is asking quite a bit as the lens has a much much wider field of view.
If the Schneider has the same image circle as the 24 Canon TS-E, it's not nearly as wide angle as the Canon, and ought to be sharper for that reason alone. I don't have any idea how the two lenses compare for image circle size.
So when I say the Canon is an excellent lens, I'm not saying it can put as sharp an image on the sensor as any of the other tilt/shift lenses Canon or others make and made in the past. I'm saying that for what it is, it's an excellent lens. Nobody else makes a T/S lens with as short a focal length as the Canon. And unless the Schneider or one of the Nikkors has a huge image circle, no other lens is as wide angle as the Canon.
It's like Harry Callahan said, "A guy's got to know his lens' limitations". ;-)