As the item description states, you can only gain 1 stack per second so only 1 stack per sweep (the sweep attacks are 0.25 seconds apart for.a 1 second total duration).

Syiccal wrote: »

Ah ok so how many stacks are needed to out perform a monster set

It’s situational. Some fights you will never lose your stacks like vAS2 but other specific boss fights like Lokestiz you will lose your stacks too often to make the kilt worthwhile. If it’s survivability you need than Iceheart may be your best option. If you are playing in an optimized group on blade, plar or warden and have high EC uptimes or if you are a Khajiit you may be over the crit cap and get better results from 2 1pc crit sets or if you are stam 1 slimecraw and 1 Kra’gh.