Steve; The Nikon or Canon close up lenses are expensive, highly-corrected 2 element creations that work very well. Their advantage: EVERYTHING works; AF, metering, etc. But there is also some marveous work done with the better-quality single element "close-up fiters", too. I'm not really sure how they work, but RAYNOX close-up lenses seem to be well-regarded.
Just avoid the $4.98 or similar "bargains",and buy from a good manufacturer, like B+W, Tiffen, or Hoya. A relatively minimal investment.
Chances are, you will not be using the item a lot, so it might meet your needs. But, if you find the quality is not what you want, or you are doing close-ups all the time, you may want to spend the money for more expensive items, or as an alternative, buy a good set of extension tubes. Kenko comes to mind, but there are others that are less expensive, and will do just as well for occasional use. But read the description...sometimes ad departments will get overly-enthusiastic in their list of capabilities. Con't be overly enthusiastic and use all three tubes in the set, then wonder why your excellent 70-210 causes the combination to droop!
Just don't be in a real hurry to either buy what you may not need, or sell the equipment, once you have it...I sold both my Nikon 6T, and AF 25mm extension tube after several years of non-use, thinking I'd have no more need for them...then I got interested in Macro photography again! Oh well; live and learn!