Unity Coroutine performances - performance

Question

I used Coroutine in Unity quite a lot in my projects, they are useful because they allow me to delay functions or do things every X seconds.
Now I know how to use them, but I don't really know what is happening in the background and I am wondering their impact on performances. Are coroutine low/fast ?
For exemple, doing things every few seconds could be done in the Update function, but it can also be done in a coroutine with WaitForSeconds or with yield return null. Are they all as efficient as the others ?
I wrote different ways here, which should do the job in theory. But which ones are the best ? If they are all the same, WaitForSeconds seems easier to read and I might prefer it.
Update way
private float shootInterval = 5f;
private float counterDeltaTime = 0f;
private void Update() {
counterDeltaTime += Time.deltaTime;
if (counterDeltaTime >= shootInterval) {
Shoot();
counterDeltaTime = 0;
}
}
Coroutine way
yield return new WaitForSeconds
private void Start() {
StartCoroutine(ShootEvery(5f));
}
private IEnumerator ShootEvery(float seconds) {
yield return new WaitForSeconds(seconds);
Shoot();
StartCoroutine(ShootEvery(seconds));
}
yield return null
private void Start() {
StartCoroutine(ShootEvery(5f));
}
private IEnumerator ShootEvery(float seconds) {
float dt = 0;
while(dt < seconds) {
yield return null;
dt += Time.deltaTime;
}
Shoot();
StartCoroutine(ShootEvery(5f));
}
Thanks for answers