A Google search on it pulls up a couple of studies, one from Germany, one from Australia appearing to show opposite results lol (also some commentary from the NZ Treasury, but not backed up from a quick scroll). It'd be interesting to know if someone's evaluated our ones.
So I guess it goes to my earlier point about feeling mixed about it. I'd suspect they have a far greater equalising effect when the market isnt so constrained that the subsidies can just can be capitalised into prices, so it might depend on the broader market a bit. And so pairing them with a massive state house building programme and allowing density with good public transport should go alongside. You know, all the stuff this government has cancelled, cut or rolled back ;)