this is a small lens which is optically very good and has IS, and is not 400 bucks. Certainly not everyone's cup of tea. I agree that this lens does not make a ton of sense on a cropper. the sigma 17-50 2.8 OS for example is used around 500, optically very good. not very large, and has os and much better range.
On full frame, if you want to have a smaller lens with IS, and the focal length works for you, then this is a good lens.
the 28mm fov is not very exciting for many photographers, instead going for a 24 or 35. I do think that people may have a difficulty flipping this lens.
However, a good deal is a good deal, if you shoot full frame, and you are looking for a small 2.8 lens with IS with excellent image quality, and 28 mm works for you.