Hovus,
That is not a supported device for the Mitel 5000. The 5000 already has an external paging interface built into it, but if the paging interface is not near the system then you may want to look at some of the Viking or Valcom devices or use the speaker wires of a 5304.
The device you may or may not need sort of depends on the application and its interface and how the customer wants to use it with the 5000.
Thanks,
TE