I haven't tried it in co op but I did pickup one during a match where I ran out of ammo, the ROF does seem a little slower and recoil is a little less.
Its still a very strong attachment for all the weapons that can use it, but defiantly weaker and probably not a worthwhile choice.
I know the patch notes said they decreased it, but it feels faster than ever in Co-op. I've also noticed I die much quicker to a RoF gun, but it could be lag. Anyone else feel like it's been increased? :/
I'm sure it's lag, I just experienced some awful lag aswell & I decided to call it a night, getting killed by 2 - 3 bullets -_-.
But I did notice the reduction with ROF on the KAL.
On the bright side I seem to be finding players mostly in my region now.