The can you afford to replace your bike mentality is the wrong way to go. Evaluate the risk of theft, the worth of your bicycle and get a lock based on that. Is there a chance it could get stolen? Yup. But a Kryptonite U doesn't take that chance to zero...it just reduces it. If you can get a small U and use the cable with it....of course that's better than a chain. If all you can afford is a chain, then that's better than a cable.