I carry two cables, both 10m. In practice I rarely need more than 10m so mostly use one, the other is there to make a 20m as a "just in case", the last case being September.
The reason I carry two is that I find coiling up one 25m cable (they all seem to come in 10m or 25m) each time can be hard going for me, holding that weight of cable in one hand. Also it takes over twice as long and these outside jobs rarely seem needing to be done on calm days with the sun shining.
A lot of continental sites have lower amperages than UK where, for example, on a CC site the normal amperage is 16a compared to often 6 or 4 on the continent. Unlikely to be of concern to a Cali owner, not the same if you are towing or driving a big white box with televisions, microwaves, ovens, etc.
Both are at 220W although on some continental sites you may find a connector difference, but a two pin to standard shielded three pin are easy to come across. I came across mine in the boot of my cali, put there by VW as standard. In practice again very rare to need it.
Again you may find reversed polarity, and there has been suggestions in the past that this could affect some charging systems. A reverse polarity tester costs a couple of quid, sold from all good places such as the forum shop,again rarely needed.
In summary, purely in my experience, 10m adequate in most circumstances, the standard connectors standard in most continental locations, the wattages the same, the amperages probably lower but in practice makes no difference to a cali owner.