the RTF(ready to fly)version has a engine that has been run it so in most cases it will fire up right away and run fairly good,after a few flights 5-10 the engine will be fully broken in and will need to be leaned out for max performance and longer flight times.
the RTF does come with the engine manual I would recomend learning it forward and backward if your going to go it alone.
in most cases stuff like making sure all nuts, bolts,and screws are tight,control surfaces are lined up and move in the right direction as well as the fuel lines are hooked up to the right spots on the tank and engine( in some cases the fuel lines have been hooked up to the wrong spots)witht the ARF you get some assembly expierence,for the same $$ will be able to upgrade since you don't need the basic sim they give you with the plane with the discounts www.towerhobbies.com you could pare down the cost even more.
I always break my orders into chunks so I can maximize there discount program no matter what plane you end up getting good luck
ARF-100$
OS 46AX-109$
4ch computer radio-140$
6ch computer radio-180$