Thank you both for your inputs on the matter.
parkfell fair point regarding the B737 vs A320 argument. He who can do more can do less. For that reason, I actually chose to fly the Piper PA-23 Aztec over the Tecnam 2006T for the multi-engine part of the course at my school. Definitely more complex to operate but also so much more to learn from, and more fun to fly too! Price was the same though so it wasn't really the same situation.
I know another guy with more or less the same background (master's degree in math/engineering) who finished his ATPL last year with a simple MCC (no JOC). And he just passed the Ryanair selection without any problem. That also explains why I may be doubtful about the necessity of the extra expense. If you're serious about knowing your stuff properly before showing up to the interviews it seems that you don't necessarily need these non compulsory additional "prep courses" to make it through. Although I believe that a fair amount of guys I studied with during ground school would definitely need it.
Booglebox I normally only need the MCC to validate my ATPL frozen licence. That's what I can get at CAE. However the JOC is not included and I can see that some companies require it to apply. There lies the questioning about if or not I should put the extra 1200€ on the table to also have it.