What shall I use instead of OnMouse_ event handlers?

I’ve build a little app where I use OnMouseDrag and OnMouseDown in some objects. I thought that it would be the best option because this methods were out of the Update method. However at compiling the app Unity says “Game scripts or other custom code contains OnMouse_ event handlers. Presence of such handlers might impact performance on handheld devices.”

So… what should I use instead of OnMouseDrag and OnMouseDown?

I’ve seen that i could use Input.GetMouseButtonDown. But to do this I will have to add an Update method to every object that has the OnMouseDown. Isn’t it worst than having the OnMouseDrag?

And, why are OnMouse events bad for the performance in on handheld devices?

if you are using mobile and you are talking about UI then using UnityEngine.EventSystems is paramount.
There are many interfaces you can implement.