I'm not exactly sure how long they are as it's pretty deceiving how much tubing goes into a coil. I don't have a CFC nor have I really researched them that much so I'm not really in the position to comment. I was just thinking that you might end up spending the $$ to get a chiller that doesn't cool enough (I'd hate to do this, that's why we ask questions here eh

) or ends up that you have to drain it really slow, but I reckon 10m would cover you (no experience with that last comment). So I'm just hoping that the transfer of heat is good enough for your given length because once it's through the chiller you can't cool it anymore really unless you throttle back the flow even more.
Where you planning a copper outer pipe?
I've been tossing up the idea of a CFC, no real reason, just need something new to build, but my brewery doesn't really allow it because of the height of the kettle. I do plan to drop to a single tier or 2 tier and incorporate a pump in the future so I'll revisit the CFC idea then.
Good luck with it. And $6 sounds like a pretty good price
Cheers, Justin