For 600 yards, a 10 to 12 power is more than enough.
Vortex makes excellent products, and I probably have about a half dozen scopes, red dots, etc from them in my safe. They also have a lifetime, no receipt warranty, that extends to ALL owners, not just the original buyer - so that makes buying them second hand less of a crap shoot.
The scope you are looking at is their lower tier glass, and probably not the best optics. If you can swing it, try to move up to their VIPER line of scopes - I have 3 of them - you won't be disappointed. I used to shoot cheaper glass, mostly Primary Arms scopes costing about $200. Once I got a used Vortex Viper and took it to the range along with another rifle with my old PA glass (that I had actually been pretty happy with) I was SHOCKED at how much more clarity there was at long ranges. The Viper made my PA scope seem like a kids pair of binoculars LOL!
Here is an Amazon link to give you an idea on pricing:
Also - there is a used one for sale right now on the forum. (IMO - unless it has been abused and looks it, buying a used Vortex is a great value, especially with their warranty - I bought all of mine used, and never had a problem):