GH status is best evaluated by testing IGF-1. Never test GH itself.
IGF-1 is what gets the job done. Your IGF-1 will be higher from SC/SQ injection than IM injections. Slow release is what is needed, what matters is time under the curve, not area under the curve.
GH promotes IGF-1 production in the liver. Higher serum GH levels simply will not lead to faster IGF-1 production as the liver is rate limited in IGF-1 production. Some people make more IGF-1 than others. You would be better off taking large GH amounts as separate injections during the day.
As with T, GH injections shutdown your own production. If you were making .4iu per day, the first .4iu that you inject does nothing. So relative benefit is there for those who really are low VS those who have decent levels.
GH is released after glucose levels start to drop and proteins are been absorbed with increasing amino acids in the blood stream [feeding response]. Your GH can be timed for that. But many simply dose at bed time when GH levels normally rise during sleep. For those who are training without GH injections, they should be aware that sugars can oppose protein utilization by impeding GH release.
Be careful with insulin, you can crash your glucose levels and one could die of a diabetic coma. Always have a major source of sugar ready to drink if you feel weakness taking over.