I've wanted a chain lock but the weight (and cost) of good ones always put me off. And yes, I ride a cheap bike so cost is relevant if the lock costs more than the bike did.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"