My group has the same question. If it only applies to a single weapon on a single model they seem quite weak. But thats also the only way it makes narrative sense?
I'm thinking of two alternative way to handle it.
- Basically treat rare items as battle honors, when your team receives them single operative has it for the rest of the campaign. It cannot be moved to another operative unless the original holder dies or is dismissed.
- Use equipment from other teams as rare equipment. Which could open up for some quite powerful combinations.