06 on is known as a WK.
The Commander is the same underneath.
Overland is still top trim iirc with the Quadradrive 2 system.
As with all things SUV it's not quite as good off road as the previous generation Grand, which in turn is not as good as the one prior etc.
If you go for the 3.0L CRD then pull the engine cover off and have a look at the oil lines going to the turbo, they commonly leak and it's £700 - £900 to fix.
Other then that Ive not heard of any other common problems.
1 person I know had the parking sensors pack up, another had a sat nav that wouldn't read a disc and another had a wiring plug corrode behind the front bumper causing the dash to light up like a christmas tree.
But I've only read one instance of each of these.
Tough starting could be an air leak or faulty injector.
Other than that check the usual, especially the 4wd system...
The prior generation had a lot of electrical problems with age, I don't know if the loom in the WK is any better than the POS one Mercedes put in the previous generation...