Applying Opti-Coat itself isn't difficult. Yes, you have to knock-down the high points, but really, unless you're completely useless, you'd be able to do it.
The harder part is the prep. You need to make your paint perfect prior to Opti-Coat. Anything underneath will be sealed in permanently. If you're comfortable with the techniques involved, knowing how to handle different issues (holograms vs swirls vs scratches etc), and the products needed to remedy those situations, then by all means have at it.
If you're not so sure, then better to have a pro do it. I myself am pretty comfortable detailing and polishing, yet I had a pro do my BMW. I'm doing my wife's CR-V myself because she's a lot less picky if I mess something up a bit
