Hey Johan,
zinc and selenium are common constituents of multi vitamin tablets and guarana is available in many forms from gum to drinks, so I don’t see how buying it for those ingredients are useful.
That only leaves the Muira puama, so if its a cheap way of getting that then why not give it a go. Its obviously aimed towards temporarily increasing chances of erections, which sounds like what you want.
Personaly I jelq hard and if anything my ability to hold an erection has increased but I also do kegels.