Personally I like to feel that I have Observers capable of operating the, increasingly technical, equipment in the most effective manner. It doesn't matter whether they be Police or Civvie, just that they use logical search processes, and the most appropriate tool for the job, to find the suspect and communicate accurately, briefly & concisely, both within & without the aircraft. This does NOT necessarily mean they have to be Police Officers , that bit's just protectionism, as is the arrest argument.
I don't think anyone is suggesting complete civilianisation of the Obs job, but a smattering in a Unit can help to keep people on their toes, especially if they have any pride in their job!
As to cost - I doubt there's much in it, but I'd rather have a Civvie concentrating on doing a good job than a Police Obs who can't understand the technology & feels he has no need to improve his knowledge.
