Thought you might like to see my hideously expensive Topflite magnetic prop balancer. It IS nice though and packs away neatly for storage!
But you really don't need it for the small size GWS props. What you DO need, if not using the "prop saver" mounting (i.e. mounting the prop on a collet prop adapter) is some means of opening out the prop centre hole to fit on the prop driver threads whilst ensuring that the hole remains properly concentric. The best way of doing this is with a prop reamer, stepped for preference but tapered if not. A badly drilled or over-size hole will inevitably cause vibration.
for a decent short tutorial on prop balancing. Generally speaking getting the blades to balance is the easy bit, getting the HUB to balance is much more fiddly.