What is the main difference between those two? They do look very similar.
Fat! Perpetum has some fat I believe. Sustained does not. Also flavor. Go to Hammer website and it is explained in more detail.
Taste! I find that the Perpetuem tastes better than the older style Sustained Energy.
Also when you mix the powder the Sustained Energy has a tendency to foam up quite a bit and leave clumps as well, whereas the Perpetuem doesn’t foam and seems to mix much better.