How many control files should I have?

Question

On the Oracle Database Appliance, the default deployment only gives you a single control file.

I find this a little puzzling. The single control file causes a policy violation in the automatically configured Enterprise Manager DB Console and Oracle's recommendation is still, as far as I can tell, that you should always have at least two control files on separate drives and file systems. Personally, I've always had three copies, just to be on the safe side.

The ODA is configured with ASM and does have a good bit of storage redundancy using triple mirrored drives. Is it OK to run with a single control file in this configuration?

Adding a second control file to the same disk group might not make much sense, would multiplexing the control files to the SSD disk group or perhaps the OS drives of each node make more sense?