Agreed, but a few text files shouldn't be a big size increase. Its the only was to provide the source to users on mobile platforms without making the source directly public. Or do you have another suggestion?
A much better and more honest approach is something like what Krita has; donations and gratis app downloads on the homepage, identical paid apps in all the app stores and a pay-what you want model for the stores that offer that. You get a larger user base, more word of mouth, more user good feelings, more fans and more potential future payers that way.
I've had multiple forms of donation buttons on my various sites and software over the years and they have never worked as good as either ads or paid software. As in, 99% difference.