I have a justarack junior. Bought because it flat-packed and was available, more than anything (and I needed to get the expanding amounts of kit off of the floor). I found some improvement by 'tuning' the bolt tension on each of the shelves a-la Mana, rapping on the timber at ach corner until it produced a similar 'thunk'.
Mass-wise, I wouldn't consider them an ideal site for an LP12, if you get my drift.
Overall, not seriously rated outside of US mags. To counter this, I know of one other forum member using these racks, with good results.
Rico - let them eat Kans.