Well I'm in Germany, so 1.) the stupid things aren't available here. And aren't all that easy to find in the US either - at least with sensible shipping prices.. (nitrohouse..
) Or, you can only find the bell and one pinion at one shop, but the second pinion somewhere else, etc..
2.) When it does come time to change them, they often won't come out without mangling up the inside of the bell..
3.) They're expensive.
I've fried plastic spurs pretty regularly, and it was almost certainly down to the stupid CB design.. I know how to mesh, shim CB's, etc..