RE: What makes Raptor 30 V2 is not for beginner ?
The bigger a heli is the more stable and easy to see it will be, so the big ones are potentially the best for training. the only thing that makes the smaller helis more popular for training is the cost. if you crash a 30 size raptor while learning to hover it will probably cost 50-60 $ US to fix it. if you crash a Fury, it will probably cost 200-300$ to fix it.
The most cost/performance effective helis will be a matter of personal choice, for me the Raptor 50 is an excelent choice. it is based on the frame of the 30 so the parts are still cheap, but being a 50 it has more power and uses bigger blades so it flies better. The Hirobo Sceadu is also available in a 50 size and is welll spoken of too. have a look at your local hobby shops and see what they carry parts for. having local parts supply is very nice.
The lowest cost good quality trainer is probably the Century Hawk it uses only small 30 size motors, so you will outgrow it, but it is also a very popular choice.