For me leash free parks are a horrible place.
You get owners who are on their phone or chatting while their dog is well beyond their reach should anything happen.
You get puppy owners who freak out when their puppy shrieks. Dogs wrestle it's natural if they let it go the puppy will learn. This is safe as long as you supervise it. If my dog encounters a puppy I am within arms reach.
You get owners who get confrontational, their dog is a saint everyone's elses dog is a demon.
If I go, I go really early in the morning less puppies and meat heads.