While I had no chance to invest a fair amount of time into it, yet, I've already noted some interesting moments.
- They do not say that you can't use your ear. Just don't do this first. The first step is visual spotting for errors.
- They structurized errors spotting a lot. There is nice list of major errors featured on GMAT exam on pp.233-250. Very well organized.
Also, I found the most of sample questions described so far to be fairly easy. Of course, they give you an idea what type of error is there, but once you know that, I found it very easy to find the right answer. I did very well on this.
More to go, stay online. Hopefully I'll find an extra hour or two tonight to work some more on this.