Context: Lens released 2012. I shoot mostly portraits, weddings, and some landscapes. Like most of my Canon lenses, I have sold this one.
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Design and Features

Practical? Sortof. Autofocus, and near macro ability. But no weather sealing or image stabilization. This lens is the smallest of all full-frame SLR lenses, which makes it a lot more practical. The almost macro ability is always a great feature to have (it's not true macro because it's not 1:1 object size to size on a 24x36mm sensor).

Image Quality

Very sharp wide open. Great value here.

Summary

The only Canon lens I have used that was not a USM lens. This is a very small lens with great image quality. But if you have a 50mm f1.8 or f1.4, this 40mm f2.8 probably won’t get much use... And, hence, why mine didn’t get used much and eventually got sold. 

...Unless you shoot macros. On that note, this is by far the cheapest good macro lens I know of. If you are interested in a lens that gets pretty close but not necessarily macro, the newer and slightly larger 50mm f1.8 STM is also inexpensive and has a much wider maximum aperture - personally I don't really have a use for a 40mm f2.8 since there are such great lens options at 35mm, but I would have a use for a 50mm f1.8. Also, with the 50mm, the manual focus ring is better, and you can get a lens hood - though the hood is expensive, and I never use hoods.