To me, it's the main feature I've been searching for in an eq program as I mainly use this setting on foobar2000 and I'm not able to find any applications aside from viper4android which requires rooting that offer this. I can't speak for others and I do not know how difficult this feature is to add or what the complications might be with the android system itself. I'm a big fan of convolvers that allow me to use personalized .wav profiles.
If you add a convolver, I will purchase the paid app without hesitation. Till that point of time, I'm sticking with wavelet because I don't really know what the benefit is of this app unless I'm overlooking something.