It supports both Core and XT in exactly the same way.
Vote buying is not an issue here. If somebody wanted to bribe miners, they could do it behind closed doors anyway. At least here everything is in the open and fair play to both sides.
It provides signals to the miners about where the economic majority is.
Still I don't see where is the freedom of choice in here when in every choice you made, there will be a reward waiting for you in the end. One side could actually have higher rewards than the other side to entice them to use it. People as we know it tend to choose on what they think is the best because of what incentives they see that they could get. Just let the economy, the miners, and the users choose what BIP they want to choose without giving them something after they have chosen.
It provides signals to the miners about where the economic majority is.
Signals of economic majority based on incentives gained because of voting?