A coffee grinder is freakin terrible, it terrorizes sweet sweet bud that someone took the time to make, it's a flower we're trying to grind. The reason you get so much "pollen" (you're actually being fooled) is that the coffee grinder pulverizes bits of the flower and leaf matter into particles that stick to the actual pollen, most of what you tap out of a coffee grinder is plant material.
That said.
I have a 4 piece grinder, I think it works great. The length of time to fill the pollen compartment depends on what you're grinding, I've seen it full after as little as a quarter. Why would you buy off ebay? I also am an addicted ebay user, anything less than $50 is
usually a waste of your time and effort. go down to the local store and pick one up for $35-40 straight cash
P.S. You do want thick blade like tines, something like solid remnants of a milling operation (each tine about 2.5-4mm x 1.5-2mm diamondish shape)
Don't buy anything with skinny pins.