To be honest, they're not very good. They're by far the worst I've experienced, not a patch on Mercedes CLS or BMW 5GT, and the ones in my old Mk1 TT are thermonuclear!
Over winter mine are on the highest setting (and coded with
OBDeleven to stay on that setting after restarting the car), but on the TT I have to turn them down after 10 minutes or my arse catches fire.