I have read that you can eat the plant itself however, and use the sap from the flower stalk raw, without processing.
I had just tried some of this from the store recently someone had got and the taste is like molassess to me, not as strong with a nice after taste but after reading that first article I believe I'm going to have a talk with them.
If I remember correctly, agave nectar is classified as a Class 3 or 4 poison.
Mildly dangerous, but not toxicly so unless you consume a lot of it or are sensitive. If you have IBS, you'd want to avoid it.
Still enough that I rarely if ever buy it anymore.
Most "sugar substitutes" are at least as bad for you as sugar. Some are much worse. You are much better off sticking to fruit and sweet vegetables as the sweet in your diet.