If you can get the GYTR weight for $100, definately go that route. That's the same price of the Steahly and it's much easier to just swap flywheels than it is to try to remove the weight if you decide you need to run without it.
If your bike has no bottom end, it helps when you're trying to pop the front wheel up from a near stop. The flywheel weight helps reduce fatigue so you can ride faster longer. I've had mixed results while hill climbing. It certainly makes the bike easier to ride while flat-tracking.
The hit doesn't do anything to help you catch up with the 4-strokes, it just makes the bike hard to ride and wears you out. It's the way the bikes make power but there is no advantage to it. Having a little snappier throttle response will rocket you out of the hole a little better, but the flywheel weight will not slow you down at all in a long straightaway.