c # – Ref. property of read-only structure or property of regular read-only structure?

I am implementing the Unity write (as in F # and other functional languages) in C #, I wrote the following code:

Read-only public structure unit: IEquatable
{
Static public read-only Unit Default = new Unit ();

public override int GetHashCode () =>
0;

public cancellation bool Equals (object obj) =>
obj is unity;

public bool Equals (Unit other) =>
true;

public static bool operator == (Left unit, Right unit) =>
true;

public static bool operator! = (Left unit, Right unit) =>
false;
}

However, I found another implementation that is quite similar to mine:

Read-only public structure unit: IEquatable
{
Private static unit _default = default;
public static ref readonly Unit Default => ref _default;

public bool Equals (Unit other) => true;
public override bool Equals (object obj) => obj is Unit;
public null int GetHashCode () => 0;
public static bool operator == (in Unit one, in Unit two) => true;
public static operator bool! = (in the Unit first, in the Unit second) => false;
}

As you can see, the main difference lies in the Default property implementation, I wonder if there is any benefit in the second implementation that takes advantage of the referee keyword.

If there is much Unit.Default to use in a code base will it save a lot of memory / GC tics?

Or is it just a micro optimization that is not worth it since a structure will be unassigned anyway at the end of the method that actually uses it?