Given that it's just a couple lines of code and has no other dependencies other than AppCompat (which nearly all apps already use), the increase in size would be negligible (<4KB).

EDIT: The AAR file is 26KB: https://jitpack.io/com/github/woheller69/FreeDroidWarn/V1.3/... But most of it looks to be from R.txt and I think that file gets deduped/compressed during app packaging?