For the record, I am against all doorframe mounted equipment like this (I especially hate ones that just 'hang on' with no mounting hardware). The reason is simple really, while it is tested to 30 Stones, you have to ask what is tested to 30 stones? I have to assume that it is the apparatus itself. While that's all well and good, the only thing that matters is how much it can support when its installed. Not all doorways are created equal and while you may be able to load that thing up with 30 stones your doorframe may only support 5 or 10 stones, or even 50 (I don't know what the actual number is btw, and it would be impossible to determine in a general sense).
Eric brings up a good point as well. They can't test durability of anything except for their piece of equipment (which I doubt they did very much of, if any). How long will your door frame hold up? What happens if you cheat a little bit and have some swinging momentum?
One thing you must always make sure of if to check that the thing is seated and there is no visible distress on the doorframe. If it were me I would do a quick 'circle check' before each and every time I grabbed a hold of the thing. What happens if, God forbid, the thing fails and you drop to the floor? Chances are your legs are bent because the thing isn't high enough to freely hang, end result is you falling straight down onto your knee caps and shins (probably going to smart….A LOT).
I don't mean to scare you Leather, but you have to be aware in order to be diligent.