[60041]

I have the Volvo tow bar on my V90 and it is fine with the AlKo hitch, as Discombobulated says, the the only difference with the AlKo ball is that it has a longer neck, which guarantees clearance for the stabiliser hitch.
With regard to the plating on the ball; this wears off very quickly when used with a stabiliser hitch, and does not adversely affect the friction pads at all: it does mean that the ball will rust when not in use, so I give the ball a smear of grease in the winter when I am not using the caravan, and clean it off with a bit of petrol before use. Over the summer, a quick wipe with steel wool is enough to take off the surface rust.