The term "Compound One" or "Compound Unity" is an invented term, of dubious origin, to liken GOD to a bunch of grapes! A bunch of grapes, they say, may be comprised of many grapes while actually being a single bunch. And from there make ridiculous false claim that in Deut 6:4 means the trinity!
This "Compound Unity theory", is a bit like trying to compare apples with oranges! And it doesn’t fit at all with the "Trinitarian" creeds. A bunch can be separated into individual grapes, (substances) and once separated, cannot ever be put back together! Anyone familiar with the Athanasian and Nicene creeds knows that among traditional "Trinitarians", this comparison would be regarded as quite unacceptable! The God of the "Trinitarian" creeds is ONE INDIVISIBLE SUBSTANCE ("ESSENCE" in the older versions of the Athanasian Creed) which cannot be separated into individual components!
Israel had just ONE LORD according to Deuteronomy 6:4, "Hear, O Israel: the LORD our God is ONE LORD:" (Not two ... not three ... ONE!).
To assert that God is actually a plurality of three separate and distinct "persons" who are co-equal, co-eternal and co-existent with one another, either portrays three individual "persons" of Deity like three members making up one family/household, OR portrays God as being one "person" with three "heads" - either of which is about as pagan and polytheistic as you can get.
God Bless!