As I have posted in the past synthelator is one of the strongest things I have ever used. It's a fucking crazy product! I am not even joking the wolverine adamantium scene comes to mind... well not quite but you get the idea

Many have reported increased endurance and energy from using it. I have always used it with a preworkout and/or synthetine/syntheselen so I can't really comment on the increased energy.
I will say if someone just wanted better endurance I wouldn't use it just for that. I think there are better alternatives. Now for it's effects on pump, vascularity and endurance then sure I would 100% recommend 1-3ml synthelator preworkout. High doses are crazy and probably best left for contest day or if you are getting pics done and want to look as freaky as possible.