Extension tubes are just hollow plastic tubes that move your lens away from the body, so a cheap set will do you pretty well. The only difference between this set and, say, the Kenko set, is the lack of electronic contacts to pass information from the lens to the body. So, aperture control and focus have to be done via the lens, not the body, and your EXIF is gonna be a little funky. But they will let you get just as close to the subject as the more expensive extension tubes will.
Be aware, though, that extension tubes mean your lens will only focus at a specific distance from the subject. You don't frame, then focus, as you would with a macro lens.
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