Berserker gives you an attack with your main weapon as bonus action.
Does it mean you would get two additional attacks with your main weapon?
As far as i know (will check later, and eventualy edit this) ... no.
Since if you are wearing the "get Bonus Action, when you have 50% HP" helm ... you also cant attack 3 times, i believe that attack have "once per turn" condition.
And if, im certainly going to suggest the same for Tieves and all Dual Wield. :P