Pierre from Betalogue reviewed MsgFIler last month. He’s written about MsgFiler in the past. He covers some of the initial bumps that often come with a major redesign of any application.
However, much to Adam Tow’s credit, I must say that, within a week of the initial release, all of the problems were solved. Adam fixed the bugs that I had encountered, and explained what I needed to do to regain the ability to undo. It was stellar service and I was quite impressed.
The article also has a good discussion on the pros and cons of moving the app to be exclusive on the Mac App Store. There have been several requests to have a non-Mac App Store version of the app, but there is currently no timetable for its release at the moment.