I think the steel/cro-mo bars are 1lb heavier than typical carbon bars. The aluminum versions weigh about the same.
The heat-treated aluminum models are very, very stiff. The steel are ridiculously stiff. Uncomfortable on bumpy tracks. But, take the $300 you saved and buy comfort elsewhere
Not an issue indoors or on smooth tracks.
EDIT: MrMinty, don't worry. At the level you are now, round bars are not holding you back. You just need time-on-task. The major benefit of "track" or "sprint" bars is their shape. Their quick sloping design allow you to do standing starts or out-of the saddle jumps without jamming your forearms into the tops of the bars and bruising them.
You cannot do this with road bars that expect your elbows to be bent:
