My first play was mostly stealth, pistol and gadgets (14 dead)..
I love the shock grenade..
Downside is 1 target limit they start with but this can be increased by upgrading (2) and then unlimited at lvl 3..
Well thrown shock trap is priceless..
In the end I had 18 shock traps (3 slots and perk for +1) though I never used them all
Also they are cheap with around 250$ a piece..
My 2nd play's goal is 0 dead and since on hard trq darts cost 20k I think ST are going to get even more usage.
Flashbang is cool as well, especially until you upgrade Shock trap to lvl 3..
After that its much simpler to throw the ST then to bother with flashbang + melee ko..
Upgrade isn't worth it I think, original duration is fine.