Ok here are lots of answers:
I have ordered several times from this website, normally on a Friday. I get the stuff at my workplace Tuesday afternoon, Wednesday morning one time that I ordered on US Labour weekend.
I have ordered Spike and it gets through customs with no problem whatsoever.
If I can remember rightly, orders over 400NZD get you pinged for gst. So far I have managed to avoid that entirely. They have all the relevant info on the customs website: customs.govt.nz