Hitting at least 3 enemies with an attack, increases your damage by 24-36% for 3 seconds.
+25-40% Cleave on Hit. Stacks 5 times.
+4.5-6% Close Range damage on Repeated Hit. Stacks 5 times.
+5-6.5% Strength for 3.5s on Close Range Kill.
You can go frag and survivalist just fine. Both sides are good. I prefer having a stronger melee kit and conserving a little ammo. Just don't use chainsword without melee nodes, it doesn't meet breakpoints without them.
Smokes are used between your team and shooters when other stuff is happening so you can focus on killing nearby threats instead of shooting gunners and shooters.