And what Airgus is forgetting to tell you is that, you need to reach an acceptable standard on the sim ride assessment.
So if you are a hot shot, then the bare minimum MCC5 will suffice.
If however you do not fall into this rare category, then the more practice you have flying a 737 variant the better chance you will have. Think about it.
JOC is not, as yet, a regulated course; Ryanair are simply saying it is entirely up to you how you prepare for the assessment.
Not all ATOs charge a premium for MCC/JOC. Do your homework carefully, and make an informed choice based on your circumstances.