I'm modifying an [open source app](http://code.google.com/p/remail-iphone/) that is non-ARC. Most of my iOS experience is with ARC enabled objective-c, so when I create and add new files to the project I tend to make them ARC compliant using [compiler flags](http://korutech.hubpages.com/hub/Adding-non-ARC-sources-to-ARC-projects) (especially when i'm faced with weird non-arc code [bugs](https://stackoverflow.com/q/11788000/766570)).

The thing that keeps me up at night is the question: how safe and reliable is it to mix arc and non-arc code in my project? When QA time comes will it be a nightmare to test for things like memory leaks and performance etc etc? Asked another way.. is it worth converting the existing non-arc code to arc code and get rid of the potential trouble?