I have not had that many problems with Hi Spec it is just these rear calipers although I have read other stories with disc run out etc. If they think 0.012" is acceptable they are wrong!
The Billet 4's I use on a front conversion but I only use their calipers not any of the other parts as I prefer to ensure the rest is correct with no issues.
Their main problem seems to be the time it takes or them to get any “special” done and here is a case that proves the point, I started this back in early November 2010 and 5 months on and still waiting.
I took the rear calipers apart and made a drawing in AutoCad and it was then easy to see where the problems lay. I then took a trip to Hi Spec to point all of the issues out to Geoff. He accepted that there was a problem and had not though of the solutions I put forward so armed with a drawing of what I thought should be done went off to redesign them.
Their point of not applying the handbrake while the foot brake is depressed is nonsense as you have no choice when driving a car on the road.
I know why there is this problem, it is due to the port design, if there is pressure in the cylinder the seal gets extruded into the port and then gets cut when the pressure is released. This is a relatively easy fix just relieve the port which is the recommended answer when a seal transitions a port.
The leak is due to the position of the two seals and when the handbrake is released the two seals over lap thus they can not seal correctly and cause the leak.
It does get very very frustrating waiting and would not mind so much if they could give a definitive date but one just gets a series of the same old lame excuses once heard repeated over the course of months start to make you wonder just what the true story is.