The danger is in the filling, not in the using.Some years ago while diving in Costa Rica I poked around the compressor room of the dive op. I notice a few AL6351 cylinders. While they had a hydro they did not have a VE. While a DOT requirement I asked that while we were diving that those cylinders not be used. The dive op honored my request.
The point being that as customer it is worth poking around the compressor room of the dive op.