The aluminum railed saddles of the 1970s did indeed crack regularly.. Many of those were made by Selle Italia especially the very popular Avocet model 3 (? or was it Model 1?) It was not a catastrophic failure though, no crashing involved... Cinelli held off initially joining in the fad for alloy rails and then (early 80s?) came out with a cast or forged aluminum undercarriage, similar to the later Selle San Marco Regal undercarriage.. . To my knowledge and experience, these did very well and did not break but were also not nearly as light. So IMO a Cinelli~Unica alloy railed saddle is not too risky a ride....
Dale Brown
Greensboro, NC