I personally think there's nothing wrong with practicing with field tips.. They can be easier to shoot with and be used on more targets and in all the indoor ranges. BUT, you do need to shoot and practice with broadheads also. Now my broadheads fly the same but the others are correct in that not all of them do. Use a quality broadhead that fits you such as magnus stinger, montecs or muzzy's..
WHEN all is said and done though you need to be sighted in using broadheads if your going to hunt with them.