I'm thinking of the jury's reaction. Smoke alarms are, as you say decades old, and people are very familiar with them. I see it being argued that PLB's are "new" "exotic" "complex" etc. and therefore require "expert" maintenance, including, for example, battery replacement.

Analogy's to other equipment, smoke detectors, AED's and probably other examples would be argued, but are not definitive and guaranteed proof and protection. Neither are licencing agreements, no matter how strongly worded.

Even if the manufacturer wins, it is expensive and they still get bad publicity of allegedly designing faulty/defective equipment that "killed people." And if they lose, it gets really expensive.

Better to avoid the risks with "non-user replaceable" batteries. That would be my recommendation, anyway.