I use leatherique's full condition/clean cycle treatment every 6 or so months, with Zaino bros leather cleaner/conditioner quick treatments every 2 months inbetween. So basically I'll use leatherique, then two months later zaino, then two months later zaino, then leatherique again.
It works like a charm.
Just remember that if it's colder than 60 degrees in your car, leather conditioner doesn't work. You need to either put a space heater inside your car until the conditioner is absorbed, or wait until it gets warmer outside.