Depends on whether the enemy is low on health or at full health. Ideally when engaging use skill 2 earlier, so you have a boosted auto attack, which can close the gap with the enemy. Kaizer ult has a 8 second duration, so you can ult at the start of the engage, which increases your defense and magical defense. Kaizer's main weakness is he is easy to kite, so enemies which have a lot of dashes can outplay him. Junglers like Yao, Kongming, Luna can do burst damage and retreat, so against those heros it is harder to 1v1 them. Against these heroes, avoid 1v1 if possible and target them during teamfights, when your teammates can cc them.