If the detangler is designed to be rinsed off you would still need to follow it up with a conditioner because if it's been specially created for detangling then it will not contain much in the way of conditioning ingredients.
That said, a detangling conditioner is designed to be both a great rinse-off detangler and a fantastic conditioner. It does both jobs.
Such a product could be used before a shampoo as a pre-poo detangler as well as after a shampoo to condition the hair.
The pre-shampoo application would be mostly washed out by the shampoo thereby making an additional post-shampoo application necessary.
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