I have a door gym. I am tall with a long reach. I semi-kip with bent legs. I can't swing back too far or the leverage won't hold the bar in place.
So - it depends on your size and how far you want to swing. When I have done pullups on a real pullup bar, I have found them to be way more comfortable. Another problem for me is that I am wider than the door when my arms are rotated out for a palms-down grip.
It is a nice piece of equipment for what it is tho'. Nice for any ring stuff too. You can also take it with you.