I’ve read up, found another thread on the very subject. Shouldn’t be a problem running dual controllers. The only hurdle should be inclusion, there is no way of putting only one of the controllers in inclusion mode. So I guess I’ll have to rely on either pulling the old stick out when including devices with the new, or pulling the new one out and including using the button on the stick. I’ve now ordered a Z-stick gen 5+, so I’ll be on the latest 
About securely included devices… I have a Danalock V3. However my wife thinks it’s too ugly and slow so she is refusing to use it and every time she locks the door using key instead it gets out of sync so I’m thinking of getting rid of it anyway. Anyone interested in buying? Anyway, that’s my only device requiring security 