We use it to diagnose a drive failure if there is no mechanical/electronic fault with the drive. In reality, it is used to diagnose every drive, but the level to which it is used depends on each drive and the fault.
Success rate is difficult to determine, because of the variance in faults that we receive. For drives with a System Area corruption, success rate is very high, but this will depend on your experience fixing SA faults also.
For a recovery specialist, the menus are very intuitive, so they should be able to get up-and-running quite quickly, provided they have a basic understanding of System Areas, etc.
As you can see, we have a considerable amount of acelab equipment and if I was unhappy with it, I would not have purchased more than one! There really is nothing else out there on the market that compares.
Our business has grown significantly over the past few years and I honestly can say that we would not be where we are without pc3k. However, it does require a lot of focus and research. You need to read the manual a number of times to understand the processes, it's not a one-click solution.
To put it another way, PC-3000 is a fantastic tool which gives you access to the drive at a low level. How good it is and what success rate it brings depends on the user!