I think many people will look at those Letters as creepy and rude. Claiming to be someone's "neighbour" when the address of the sender is NOWHERE near you is obviously a Sales Ploy and is deceitful.
I would doubt there ever will be any notable success, perhaps not even any measurable success, for the JW's with this waste of time effort and cash, but the Org does NOT care.
The Org evidently does not want new recruits, it wants to shrink to a core of loyal JW's, but it wants to keep the present members busy so they don't start to drift away. Anything that makes them feel as though they are doing something worthwhile.