Pen machines are fine if you use your head while using them. I have seen guys tattoo with them and without paying attention or thinking while they are wiping they are holding it off to the side close to upside down and due to gravity you are going to get filth and ink up in the machine. I have used several different pen type machines with both membrane and non membrane cartridges and am 100% conscience of not holding the machine at angles that would invite back flow or touching the part of the cartridges that goes into the grip and have never had any issues. I set up another tray away from my work station that I set my cartridges on so they don't accidentally roll into each other or get ink dripped on them and whatnot. I have taken these things apart to inspect, clean and re grease and never have I found any trace of ink. If you aren't a slob while tattooing to where your work station looks like a pigsty when you're done, running the machine too high that you're spraying ink around and you pay attention to not tipping the machine upside down there really aren't any issues.