Allowing HA hardware revision mismatch on 60E, any issues?

[journeyman]

We are now receiving a new hardware revision of the FGT 60E (old part number P18816-01, new P18816-03), and of course I have a mismatched pair on my desk from which to build a cluster. My understanding is that the above represents a mismatch and that

exec ha ignore-hardware-revision enable

exec ha ignore-hardware-revision status # view current settingallows a ha cluster to form when the system part number differs. However I do not see the command available (it does not autocomplete). We run 5.4.4. It also doesn't autocomplete or even work when manually entered in 5.6.3 either. This link  says the command is not visible in 5.4 if there is no hardware revision. Maintainability is an issue because the setting is not part of the configuration file.

[ol]

(Sanity check) The part numbers above represent a hardware revision delta, right?

Any idea why the command doesn't work in 5.6.3, which is on the newer hardware?

Is this feature / functionality a normal one to use, or should it be used as a last resort in exceptional cases?

Happy to hear your experience / recommendations...[/ol]