I've seen users who have claimed that lag happens as the little disc gets used/dirty but I've had mine for a few weeks now and have taken notes 3-4 hours per day using it and have yet to experience any lag at all. No screen damage either (not sure why they would but again, a few users have claimed that). I don't use a screen protector and, as I stated, I'm in VERY dirty environments all day long. In an office/classroom setting, have to imagine performance would be as good if not better than what I've experienced.
Really the best in the market currently for taking handwritten notes IMO.
They have magnets in the tip, which attaches it to the screen for precise writing