1) I believe the studies cited use a full-spectrum tribulus and not an extract. If they use an extract, it's not mentioned.
2) Studies don't dispute the sexual benefits received from tribulus supplementation.
3) What most studies say, is that tribulus is not anabolic.
4) From what i understand, most of the extracted substances are progesterone-mimics. So, even if they don't raise testosterone, they should increase the T-to-E ratio, which does have benefits. Which would probably most likely be a "leaning out" effect, or a recomp, as opposed to a weight gain due to a huge increase in mass.
Sorry about the numbered format, but I "think" better this way. Also, these are deductions on my part, and may not be altogether correct.