Lovely photos. Can you tell me a litlt more about your setup? Just bought my first SLR - a D5200. So have you used these macro tubes with a kit lens or something a little more special?
Thanks! I have a canon 550D. The dandelion (or whatever the puffy flower thing is called) was shot with the kit lens on the tubes, but because the kit lens is already pretty soft, I usually use a 50mm f1.8 prime (the canon "nifty fifty" cheap but sharp EF lens). Those are my only 2 lenses right now, as I can't afford to spend £600 on news lenses when I feel like it! Hence the cheapo tubes instead of a decent macro lens.
It works fairly well for a couple of reasons: using extension tubes means you are only using the centre of the lens (more extension means you are using less and less glass), which is usually the sharpest bit anyway so it sort of balances out. Also, sticking a light prime on the end of cheap plastic tubes is better than a chunky zoom lens. Primes are also really great for the large apertures when you aren't doing macro.
While I don't know if Nikon have an equivalent of the nifty fifty, a sharp fast prime on a budget is a good buy.
In short, yes, you could use these £26 extension tubes on your kit lens, but ideally you would have a long prime at least 50mm. Aperture won't matter for macro since you'll be stopping down the lens to get more DOF anyway (super super small DOF when you are 2in away). Ideally you would also have a tripod for subjects that don't fly away because tiny movements can blur a picture. The small aperture usually means you will be shooting longer exposures than normal, so only bright sun is really workable for handheld. It's challenging, but I'm really enjoying it!
Hope that helps!