The 300 PRC is a great cartridge, especially if you are hunting/target shooting at longer range. It really shines above the 300WM if you are shooting heavier projectiles. If your want to shoot 180's or maybe even 200's, the Win Mag would be just fine if not a better choice. If you want to shoot 225's or 245's the PRC is the way to go. There is decent factory ammo available so being a handloader is not a must. Recoil energy will be somewhere around 15% give or take more than the 300WM.
As far as the Christensen go, it seems that you have a good chance of getting a fantastic one and an equally good chance of getting a bad one. I'd really look into why he is selling it.