Yeah, test it in Final Cut Pro X and optimize for this host! In my experience it is quite a bad/different host for audio plugins (i.e. it might crash, even if your plugin is a totally valid AU and rock solid in every other host).
If you move the play-head and the option ‘Audio Skimming’ is on (on by default), for each audio snippet you hear (approx. 10 a second) a new instance of your plugin will be created and destroyed. This is quite a stress test for your plugin.
A 30 day trial version of Final Cut Pro X is available at https://www.apple.com/final-cut-pro/trial/. On each minor update of FCPX you can run the new trial version for another 30 days. Or ask Apple to get the full version for testing. You might be lucky.
@anthony-nicholls : Does automation in FCPX with your plugin really work? It seems that JUCE has an issue with automation in FCPX. Please take a look at my earlier post about it: AAX plugin, automation gets all messy after a while
Sadly it didn’t got any attention by the JUCE devs.