The app is stable and should not make any problems on ICS/JB ROMs. The installation procedure is usual: flash the ZIP in recovery mode.
Don't forget to make a backup before flashing!
If the for some reason the CWM zip didn't work for you or the Keyboard doesn't appear in settings do this:
- Decompress the zip file.
- Ignore the META-INF folder
- In the app folder, you'll find textinput-chn.apk (Mandarin Chinese keyboard) and textinput-tng.apk (English keyboard).
- You can move one or both into /system/app folder with ES File Manager/root explorer/etc. (or adb)
- Move lib/libXT9Engine into /system/lib
- Move usr/xt9 into /system/usr
- Reboot. If you still don't see the keyboard in your settings, install the apk with your file manager which should work with the libraries installed.