12 and 14 are key sizes.... I wouldn't even look at a set that didn't include those.
12 and 14 are key sizes for Japanese cars only. 12mm is the head size for a JIS (Japanese Industrial Std) M8 bolt. 14mm is JIS head size for M10.
I work almost exclusively on German cars. DIN (German Industrial Std) for an M8 is 13mm. M10 needs a 17mm.
ISO/ANSI fasteners are creeping onto German products. They are using some coarse thread M10 bolts which have 16mm heads. Ditto for M12. DIN for M12 fine is 19mm. ANSI/ISO coarse M12 has an 18mm head. That's where the 16/18s are coming from.
So: We can fairly safely predict what wrenches we will need for specific vehicles based on the bolt studs. GENERALLY, 12 and 14mm wrenches are only reqd on Japanese cars or cars that consume Japanese parts (which could include Korean vehicles, rebadged US mark vehicles).
That said, I will most likely fill in my XHDRs in time!!! European car makers (like all car makers) keep getting bought out by other makers and some foreign parts find their way onto domestic (euro platforms). So I agree it is preferable to have every size if you can.
I guess my point was, you can buy Chinese double box ratchets from E-Z red or the equiv for $150 for a set. But they don't have non ratcheting sides or the super strong, super thin box ends the Snap Ons have. For an extra $100, not hundreds of dollars, I found a SO set on ebay. Those deals are out there for folks who are interested.