It's probably a good deal. I remember them being about $130, but haven't checked prices lately. I'd definately go with the Kenko tubes though, and you'll want the whole set.

What your doing is building a macro lens. Lenses like the 60mm macro have the extension built into them with a floating element. What you're doing is manually adding that extension. All three Kenko rings will give you a magnification of about 1.3 to 1, more than the 60mm macro has by itself. At about 1 to 1 your focusing distance will be about 2.75 inches. At some point you'll probably want more magnification and/or more working distance. At that time, you'll want to add a 2x teleconverter to the mix. This will give you up to 2.6 to 1 magnification, or double your working distance. 2.6 to one is pretty much the practical max for most field work. I only work up to about 3 to 1.

Good luck,

--Jeff