(I) It works properly on most devices, but "shake to answer" action may doesn't work properly in cooked ROMs by some manufacturers to include a layer of software that modifies standard Android behavior.
Historical tested devices:
- Huawei U8650 (GingerBread 2.3.6) - OK
- LG Nexus 4 (JellyBean 4.2.2) - OK
- Samsung Galaxy mini (GingerBread 2.3.3) - OK
- Sony-Ericsson Xperia mini (ceCreamSandwich 4.0.1) - OK
- HTC Explorer (GingerBread 2.3.5) - No work
- HTC Explorer (Cyanogenmod 9 - IceCreamSandwich 4.0.4) - OK
- Samsung Galaxy ACE/Y/S2/S3 - OK
- Samsung Galaxy S4 - No work in some models
- Sony-Ericsson Xperia S - OK
- ZTE - No work in same models
- LG L9 - OK
(II) Because it uses system functions (phone state access control, audio and unlock the screen), the app makes use of several low-level permissions that the user must accept at the time of installation.
(III) To use the function of "Voice Synthesis" is necessary that is activated on the phone:
Settings> Voice Input & Output> Voice Synthesis Settings