Depends what purpose you want your strike indicator to serve. If you need it to double as a float and keep your fly off bottom, choose the bigger ones such as the thingamabobbers. If it's there merely to indicate a hit, use the small cheap ones artimus suggested.
I'm not sur about the New Zealand gadget; you can achieve the same effect by folding your line, inserting it up through the tubing, putting a piece of yarn in the line loop, and pulling it back through. You can also attach beads to your line this way with an elastic, enabling you to take them on and off without removing your hook.