I own one but i use it only occasionally on the big breakouts. The device instructions says there isn't that much pain, but when i use it i feel like it's burning my pimple but it's okay at least not as painful as getting laser....
After the 2min treatment with Zeno the area you put the zeno on will be red for a few hours, BUT during that time you will feel the pimple becoming not as sensitive and beginning to die even though the skin is still really red.
The instructions in Zeno say that the device is only for those pimples that DON'T have those pus inside but i tried it on the ones with pus anyways and basically what Zeno did was fast forward the stages of pimple development and by the next day the pimple on my face had dried up to the point where the skin was naturally forcing out the pus (or that little hard white thing in the middle of pimples--i call it a rice grain haha). So it wasn't too bad but i would generally only use this device on really big pimples.