FSH/LH are what triggers your balls to do their thing. This is shut down on exogenous testosterone. Gonadorelin stimulates the release of FSH/LH while hCG mimics LH and keeps your balls going. Both keep your balls going, but gonadorelin has such a short life and because it simply triggers your own pulsatile release of hormone, it needs multiple daily doses to be effective. In clinical trials it was run on a pump for this reason. hCG is generally considered to be more effective.