There is an amount of liability in everything we do; aluminum pistons have been used in diesels for decades with good results and were, infact, used first to help deal with unbalance. The Listeriod exhaust temperatures are so low that it is hard for me to imagine piston damage for heat at any reasonable power level. Scuffing and seizure are common even with cast iron pistons if care isn't taken during running. Lube and break in issues are far more important for long life than materials of construction on a low specific output slow speed engine.
There are always backups in marine service, too, so that if the Listeroid should fail for ANY reason there is another generator and another air compressor. I think AN engine of ANY manufacture is a liability if it is the sole source of power for a life support system, but thankfully most applications are not life support.
In any case, the 14/1 Metro I got from Sam Crosby is not a hopper. When running on a shipping skid in the shop it slowly precessed in a circle, taking about two hours to transit it's course. Once the whole assembly was ready to install I test ran it for a week under load with no precession or hop while resting on four pieces of rubber on the concrete floor.
Standing by, ready for flames and criticism,
George