He get's a 6+ armoursave (and 6++ wardsave if he's on a Luminark). He still has a 90* LoS, it's not a Screaming Bell, it's a regular chariot.
It also eats up 120/130 pts of your Lord-allowance instead of your Rare-allowance.
(Down- or upside, it depends on what sort of points you lack the most.)
The downside is that he will get a big red crosshair on his forehead - any cannon/stonethrower/template that hits the chariot will hit him as well.
I would never,
ever put my Wizardlord on a Hurricanum/Luminark.
Better mobility?
A wizard can march and cast spells, so their movement is the same.
In all-cav lists you're better of mounting him on a barded warhorse and place him in a unit of Knights.