I've had 2, both Convertibles, one a 645 and the other 650....great cars, but I think a bit long in the tooth now....I'd go for a Range Rover Sport instead....
No mechanical issues whatsoever, just a faulty roof sensor on my first one, which lasted 18 months!! Servicing, tyres etc aren't cheap though....stay away from black and cream leather ones, they can look tired very quickly...