There is more than one way to skin a cat.
I don't see a problem whether two switches are mechanically linked or are independent. They both give the same level of safety.
In the Sim we would get a trim runaway and hold the trim wheel to dis-engage both systems, then re-engage one at a time to see which system was at fault. Sometimes it would be a dual failure.
As for reliability, I don't remember there being a problem on the A300. I don't know about the later Airbuses, A320 and on.