Is the deal actually a good one for the Serbs?

As I understand it you're selling your natural resource rights to the Russians. Since they already are an exporter of oil/gas it means they intend to sell what they get from Serbia at a profit. Implying that if you guys could sell the resources on your own you would make more than the Russians are giving you.

Is it just that this way you get cash up front instead of having to pay for infrastructure up front?