Have you noticed how the M500 scares the mightiest of tecchies? It remains one of my best loved 'secret weapons'!
Whether you get phase problems using external hardware for parallel compression is very much down to how accurately the latency is being calculated, and has little to do with the external hardware itself, (assuming it is analogue). I often find it best to record external parallel compression and align it manually to sample accuracy.
An Eagle for an Emperor, A Kestrel for a Knave.