I bought a GReddy Counter Weight Shift Knob for my Mazda5! Quality stuff.
The stock Mazda5 shift knob weights about 10 ounces. The GReddy CW knob weights 13.5 ounces. The stock knob is actually pretty heavy for a factory knob, but I don't like its length and prefer a heavier, shorter knob.
A weighted knob feels great! Its weights help smoothen shifting.
The GReddy Counter Weight Knob
Before and after