Been playing a lot of world of tanks recently. Fun game, addictive, lots of things to master.
They are really, really good at draining your pocket in teeny, tiny little drips and drabs.
That said, you can choose to pay or not.
Personally, I don't see how I'm going to get set up with a Bert the Avenger unless I shell out fifteen bucks to convert free XP - my brain would die if I had to grind the XP via the Bishop. Same with the ISU-152. Gots me an IS-2 as an XP machine for Bert and as a credit machine for my coffee in the ELC.
I still suck though.