Alex nailed it. The GRAS designation is worth paying attention to, it’s a meaningful distinction in terms of safety research compared to many other compounds in this space.

From a research standpoint the mechanisms are similar (both appear to act on the fat-specific receptor rather than general GH receptors, which is why neither produces the insulin resistance concerns associated with full hGH). The modification in AOD-9604 theoretically improves bioavailability but comparing them head-to-head in human studies is difficult since most data is in animal models.