I agree that this is THE best single mono/stereo track editor and mastering solution among every currently available Mac dittos. I purchased it one and a half year ago, and I still think it's totally awesome; rock solid stable, powerful and fast (wicked fast!).
There are two (2 little details that I'd like to humbly express my discontent in). Remember, these are my ONLY objections, all other audio programs (I have tested them all) in this genre has tons of things I could complain about, so. Anyway, here are my concerns:
1.) Every time that I want to create a new document, say if I want to save some part of the current file into a new sketch document, I have to first SAVE THE NEW DOCUMENT, before being able to use it... That is honestly quite irritating, since I'm always ending up with LOTS of documents, many of which I never really wanted to save. This is what I can't seem to understand why DSP-Quattro does it. Where DSP-Quattro beats the competition by miles, here's where it really looses ground. All other applications let you create a new document, do whatever you want to do in it, and finally DECIDE, whether you want to save it or not. :(
2.) I think that the copy/paste functions are quite fuzzy. It isn't like, normally, when you just select a part of the sound that you want to copy, then press Command-C for copy and Command-P for paste. Instead you have to use another combination. Maybe it's just me who have a concern about this, but I think that the copy/paste routine has to conform to more standardized and common operation.
But all-in-all, if you are to buy a great, classy sound editor and want the real stuff, buy this one. It won't let you down and in comparison to the others, this application still stands its ground as being number one.