When exactly do you tech to Grenades & Zooks/bars ?
I hear with some commanders you don't tech to zooks/bars at all? When does this apply.
Also, are Bars worth upgrading?
You tech those upgrades AFTER you get Lieutenant or Captain. (Getting it beforehand will delay both options)
I don't know about the commanders, but it's possibly referring to the Airborne Company since Paratroopers have the option of 2x LMGs or Thompsons. Another commander would be Infantry Company due to the M1919s.
As for upgrading Bars, it usually depends on the situation. Though the Bars have better accuracy on the move, so that had to be taken into account.