How does it works?
UNO works in the "old skool" way, it themes Mac OS X in the "hardcore" way.
This means that, instead of leaving a process permanently running in the background waiting for your application to be launched and patching it (what can affect stability and performance), UNO runs once to install and once to uninstall, and works by actually replacing some graphic resources (after backing them up).
Does it affects system performance or stability?
No. No process is left runnig in the background. And UNO leaves the resources files with the correct permissions, owner and group.
Hum.. Replacing system files. Is it safe?
Crossing the street. Hum.. Is it safe?
It has its risks, we are replacing system files. But UNO sets the correct permissions for files, checks for OS version compatibility, iTunes version, processor architecture, and if something goes wrong you still have "guifix" to rescue you.
Also, introduced in version 1.5, UNO checks the integrity of the crucial files through md5 and crc32 verification.
No common problems are known.