They are pretty much the same, with perhaps some slight differences in flexibility as you said (maximum stay, cancellation fee, etc.), but the general categorization is that YBHK are the most flexible, and you can upgrade yourself with miles. MLV has less flexibility (no mileage upgrades) yet are much cheaper and earn the same amount of miles, and thus quite popular. SNQO earns no miles and suits infrequent travelers or those with no oneworld/ CX loyalty, but is not popular among FTers (unless its an insanely cheap deal).

Differences between economy flex and restricted economy may vary from route to route, so it is best to check on the CX website for your specific trip.