eBay and Craigslist finds

You could never swap chainring, which you're aware of.

Also sometimes the weld holding the arm to the ring loosens so you could be spinning but not moving.

At 8.99 consider them disposible, but you should probably put your cash towards someting better.

I bought a set of these, they are worth what you pay for them, not very much. They're not round and usually pretty scuffed up. Fine for polo I suppose.