The 28/35 combo finder stands 14mm above the camera top plate, and stands 1 cm higher than the top of the shutter speed dial on the T. It's 15mm wide, about 3/4 the width of the hot shoe base, and a metal body. Mine's small enough that it eluded me on a first-pass look for it to measure. It rattles around in a 35mm film canister. I can just make out the 28mm frames with eyeglasses, which fit fairly close to my face.
Magnification is at or very near 0.5x. Sometimes that makes the two framesets seem a bit crowded. It does have parallax marks for both frames. The rubber surround on the back is like a square grommet, and tends to come loose, especially when it rubs against something as when going in and out of a camera bag, so be careful with that. I'm considering gluing mine at one or two points. The front element is completely exposed, not set back in a frame, so it's prone to fingerprints. It's as bright and clear as the other V/C finders, and significantly smaller than the other finders, with a much lower profile; enough to make the difference between being pocketable and not. I'd buy one again for the same reasons you want one, and I don't even have a 35mm lens, only 40mm and 28mm.