Anyone using this: Magic AB  price $52.99

That would be useful for djaying 6 songs into a mash up like this:
 

Using as a standard part of my workflow.

Yup! Great tool! Switching between two mixes with minimum time between mixes is a very powerful way to check your levels. It can be done other ways but this really improves the workflow in my opinion.

I recommend you get this one and keep it on your master bus.

I think i will do that.. then i just need some great sounding music, as reference's.
it will simplify comparison's.

Mod Bod
I recommend you get this one and keep it on your master bus.

I send my Master bus to my Reference bus, where I have Magic AB. The Reference bus goes to my audio card. When Magic AB is off it's just a pass through and has no effect on what gets to the soundcard.

This way I can have effects on the Master Bus or its ProChannel and Magic AB ( on my Reference bus) hears everything that comes out of the master, fully effected. I use that to compare my master to the reference tracks.

Thanks for this! I was jonesing to pick up a plugin and didn't want to repeat something I already had - like another EQ or compressor. This adds a brand new improvement to my workflow, thanks! :)