Those are just the Zeikos relabeled under yet another brand name. Plastic barrels (Kenko are metal)... What's shown at the link are the metal bayonet... the more expensive version of the Zeikos tubes. Price seems quite good... more like that of the plastic bayonet mount version.

I wouldn't rate them "better" than the Kenko... But I suppose it depends upon your usage. These are probably fine for someone wanting to use them very occasionally and not using them with particularly heavy lenses or cameras. The cheaper version with plastic bayonets, I'd probably only use with very lightweight lenses.

For heavier gear, long-term use and durability, I'd want the Kenko (or in your case, the Nikon tubes... in my case the Canon). After all, the metal ones should last pretty much forever... There are no optics and few moving parts to wear out. More expensive up front, sure... But I've been using the same tubes (3 Canon and the Kenko set) for at least ten years.

Not sure if the plastic ones would hold up as well. But they may be just fine for many folks.

Another possibility is a variable macro extension tube, which is called a macro "helicoid". There's one being made now in Canon and Nikon mount. Not sure the quality of it, seems like a lot of plastic (http://www.amazon.com/ProOPTIC-Helicoid-Macro-Zoomer-Nikon/dp/B00888FXOO/ref=sr_1_6?s=electronics&ie=UTF8&qid=1408118203&sr=1-6).

The problem with a macro helicoid like this is that it only offers long to very long extension... 46mm minimum and adjustable for up to 68mm. Wouldn't be very useful with shorter focal length lenses. I've never used the somewhat plasticky helicoid shown above... I've used helicoids from different manufacturers in other systems.

There are also macro bellows, which also are essentially variable length extension tubes. (http://www.amazon.com/CowboyStudio-Focusing-Slider-Bellows-Cameras/dp/B006B7R4LY/ref=sr_1_2?s=electronics&ie=UTF8&qid=1408118526&sr=1-2) These give long to very, very long extension, potentially giving ultra high levels of magnification (5:1 or 5X lifesize is possible with some lenses on bellows). Most bellows do not support auto focus or electronic aperture control... at least the reasonably affordable ones don't. Novoflex is one manufacturer that makes bellows in versions that support AF and electronic aperture control, but they are very expensive comparatively.

I use Canon gear instead of Nikon, but have the Kenko tube set to use with it. I also have a few Canon OEM tubes.

The Kenko tubes are top quality, equal to what Canon themselves offer, but cheaper when you buy the set. Canon only sells individual tubes... 12mm for about $85 and 25mm for roughly $140, "street" prices new. The Kenko set includes 12mm, 20mm and 36mm, and currently is available new for $178 in the Canon mount.

There are cheaper. Both Opteka and Zeikos make sets that sell for $100 or less, but are a lot more plasticky than the OEM or Kenko. Note: the Zeikos sell relabeled under many brand names including Bower, Vivitar, ProOptic (Adorama house brand), Dot Line, Fotodiox and more.

There are also two grades of the Zeikos... the $75-100 version has metal bayonet mounts, while the sub-$60 set has plastic bayonets. Might be okay for occasional use, but you'll have to judge for yourself if you'll trust your camera and lens to them!

I have only seen photos of the Opteka... they are fairly new and appear okay. Their set includes 12mm, 20mm and 36mm, same as Kenko.

The Zeikos (etc.) set includes 13m, 21mm and 31mm tubes. Kind of odd sizes, but that's unlikely to be a problem. One thing I dislike about the Zeikos is they use a protruding lever to release the lens latching mechanism. To me that seems a little risky... I can imagine accidentally unlatching a lens and dropping it. The Canon and Kenko I use have a somewhat recessed button release, which seems safer to me. (I've had some teleconverters and macro tubes in the past, used with other camera systems, that had a lever release similar to the Zeikos design... I had a couple close calls with them, though no real disasters.)

You'll also find very inexpensive and simple extension tube sets, often for $20 or less. These have no electronic contacts to support auto focus and, on many modern lenses, aperture control. IMO, it's okay to focus macro shots manually, but lack of control over the aperture is a PITA and unacceptable. Might be okay though, if using vintage style lenses with a built-in aperture control ring right on the lens itself.