Solid Hardwood, Engineered and Laminate Flooring - Liquid floor leveler prior to install. Questions

I am finishing part of my basement and I know my floor down there isnt exatly level, so I thought about getting that floor leveler stuff I saw at Lowes and Home Depot.

1) Does this stuff work?

2) I have a big hole in my floor where I had to jack hammer out to restub the plumbing and I am about to fill it in with concrete again. does cement expand any when it dries? Meaning, should I leave it just shy of level with the rest of the floor so that then when I pour this leveler stuff in, it just takes care of the difference so I dont have to grind any cement down?

3) Any tricks to using this stuff? How do I do it?

Thanks

Self leveler is not DIY friendly. Don't even think about mixing it in 5 gallon buckets. You need a 55 gallon drum, and a big mixer!!! Or have a mixing pump.

Actually any cement shrinks as the water molicule dehydrates from the mix.