First, quality of product is critical to explore because, as with any manufactured product, there is the potential for contaminants, and intentionally added ingredients which would jeopardize the quality of the end product thereby potentially creating health risks.
Second, the issue of quantity with any food is significant, but it seems to be the key piece with sweeteners and their negative impact on one's health. The core difference between sugar and agave, is a higher content of fructose (commonly known as "fruit sugar"). A higher fructose content helps lower the glycemic index of agave nectar versus table sugar. A lower glycemic index (GI) is good, right? Well, yes and no; and here we return to the issue of quantity. High amounts of fructose have been shown to increase triglycerides (a part of blood cholesterol) in individuals with insulin resistance, and it may also be implicated in non-alcohol fatty liver disease. High amounts of glucose are implicated in insulin resistance, obesity, heart disease and challenging the immune system. From where I stand, neither one of these then sounds all that great, right? And yet, there is no evidence that small amounts of glucose or small amounts of fructose present these risks.
One other food development issue may tip the balance in favor of agave and that is that it is sweeter than sugar so we are able to achieve a higher sweetness profile using less. So that nets us out at small amounts of agave syrup which is lower GI than table sugar is not a health risk, and indeed may be better for many.