When you take testosterone you suppress your LH production. If you then take HCG you will turn the testes back on and that HCG will increase testosterone further.
If you take HCG by itself, that will increase testosterone. But that will then cause LH to be reduced and the gains will be somewhat erased. If you took large amounts of HCG, then you could increase testosterone somewhat. But if you use too much, the LH receptors in the testes will down regulate and that is not a good outcome.
It does not sound like a simple solution. Feedback systems aways want to swamp your gains.
And as test increases, so does estrogen, and soon after SHBG increases. So the test is lost to SHBG and to E.
It would work well I expect for someone who was low on testosterone from a lack of LH production.
If you are a young guy and your pituitary and testes are working normally, then HCG long term could have some negative effects on getting your system to make ample amounts of LH on its own, just as with taking testosterone.
You can take enough gear to swamp feedback systems. Less than that simply replaces your own production with gear. So little can equal nothing. If you make the feedback system see less of a feedback signal, then the system will increase test itself. This can be from reduction of the estrogen levels (aromatization), or antagonists that interfere with the feedback system’s estrogen receptors from seeing the levels of estrogen. Too little estrogen and cholesterol goes bad and libido can suffer. Too much estrogen and libido can suffer.
If you are going to stick yourself with needles anyways, that could be less expensive than supplements.