Easy-to-Use OnyX Alternative Applications. OnyX for Mac from Titanium Software is a power user’s dream, yet an average user won’t be able to put OnyX through its paces. It comes an overwhelming set of features wrapped in a simplistic interface, which makes figuring out what does what a brainteaser.
Running OnyX on my Mac will speed it up That's a generalization; there's no such thing as just 'running Onyx' because it does a lot of different things that must each be run individually. Some features are just extra settings that don't have any effect on speed, especially the cosmetic ones. Some are diagnostic in that there's no reason to use those features unless you notice something's wrong. Some are maintenance features that might make your Mac faster, but only if it's slow because something's in a bad state. Some Onyx features might actually slow down your Mac.
For example, some users think they ought to 'clean their caches' (which is one thing Onyx can do). But the purpose of caches is to speed things up. Cleaning caches usually makes the Mac slower for a while until the caches can be built back up.
So cache cleaning is only there to resolve problems with the cache, not to guarantee that you will 'speed things up.' For a normally functioning Mac, Onyx probably won't make any difference in speed. Onyx is a wonderful tool, though. Using Onyx can be a good idea if you are enough of a power user that you know why each setting is there, you know what it is you would specifically like to change about your Mac, and you know which specific Onyx settings will do that and which ones will not.