Subject to the provisions of Section 6325, the benefits or rights resulting from the designation are payable or transferable directly to the trustee, without becoming subject to administration, upon or at any time after admission of the designator’s will to probate. A designation pursuant to this chapter does not have the effect of naming a trustee of a separate inter vivos trust but the rights and benefits or the proceeds thereof when paid to the trustee are, or become a part of, the testamentary trust or trusts established pursuant to the designator’s will or shall be added to an inter vivos trust or trusts if the disposition is governed by Section 6300.