I never noticed anything wrong with it, then again, I never used it to adjust the size more than a few pixels. If I were to go with drastic measures, I'd usually go with switching out the FontObject with another bigger variant. In this example, switching out
NumberFontNormal with
NumberFontNormalHuge increases the size to 30px.
Code:
/run MainMenuBarBackpackButtonCount:SetFontObject(NumberFontNormalHuge);