They are safe to stack together as there is no interaction between them. However, as @steve has well pointed out, you won't get a noticeable effect with them. I have tried those before, and did not notice anything at all. HCGenerate is definitely the king of natty test boosters, and I really feel the difference when taking it, so I can truly vouch for its effectiveness. As for the fat burners, I would recommend trying out the N2Slin - it is a potent nutrient partitioner, which will redistribute your insulin into the muscles instead of fat. It is quite effective - me and my wife we have used it in multiple ocassions, and it works great.