Different developers may or may not rely upon data mining your personal info so your question is a bit vague. It depends on just which app you're looking into. Some won't and are safe to install and use, some aren't. Plus, something like a lock screen app involves a deeper level of integration with the base Android install on your phone, so its potential risk is more than say, a third-party calculator app that requires no extra permissions to be enabled.
Data mining is almost impossible to avoid when it involves an Android smartphone. Google is always doing it so that's a given, most carriers (cellular) and ISPs (broadband) monitor your online access, and the more third-party apps you install the more potential there's going to be for other services to be collecting data about you. Personally I just use the lock screen that's already integral to Android but that's just my own preference, I already just assume Google's oversight is there. Installing apps that duplicate existing services should at least involve a conscious choice to do so.
