Blooming/Flowering Nute Additions?

I've read many of the thread here and listened to many of the Zandor's grow reports. The latest thread that Latewood posted has been especially helpful in the area of my question. However, I'm still a bit confused with all of the bloom/flower enhansers out there and when to use them.

I'm about 1-2 weeks from turning back my lights to 12/12. I've been feeding my plant GH 3-part (grow, micro, bloom) with Hygrozyme, Liquid Karma and Cal-mag.

Recently I've been hearing a lot about Gravity, Bud Blood, Big Bud and Over Drive but I'm not quite sure of a couple of things:

1) I know the Bud Blood I use as a transition correct. But what about the Big Bud, Over Drive and Gravity. Are all of these basically the same thing?

2) Do I use these addtions in conjuction with my regular GH 3-part?

3) When is Big bud or other bud enhansers added? It says 3-4 weeks. Is that 3-4weeks prior to harvest? Or only use for 3-4 weeks as soon as I set my lights to 12/12?

4) Do they really make a big difference?

5) Is there anything else you use to enhance the size, resen etc of your followers?

Sorry if these seem like stupid questions. I'm a bit new to additions to normal feeding. I just stared using Liquid Karma and Hygrozyme based on Latewoods post. So I thank you for the quality of the info you are providing. It is helping a lot.